Online Etymology Dictionary

religion (n.): c. 1200, "state of life bound by monastic vows," also "conduct indicating a belief in a divine power," from Anglo-French religiun (11c.), Old French religion "piety, devotion; religious community," and directly from Latin religionem (nominative religio) "respect for what is sacred, reverence for the gods; conscientiousness, sense of right, moral obligation; fear of the gods; divine service, religious observance; a religion, a faith, a mode of worship, cult; sanctity, holiness," in Late Latin "monastic life" (5c.).

According to Cicero derived from relegere "go through again" (in reading or in thought), from re- "again" (see re-) + legere "read" (see lecture (n.)). However, popular etymology among the later ancients (Servius, Lactantius, Augustine) and the interpretation of many modern writers connects it with religare "to bind fast" (see rely), via notion of "place an obligation on," or "bond between humans and gods." In that case, the re- would be intensive. Another possible origin is religiens "careful," opposite of negligens. In English, meaning "particular system of faith" is recorded from c. 1300; sense of "recognition of and allegiance in manner of life (perceived as justly due) to a higher, unseen power or powers" is from 1530s.

To hold, therefore, that there is no difference in matters of religion between forms that are unlike each other, and even contrary to each other, most clearly leads in the end to the rejection of all religion in both theory and practice. And this is the same thing as atheism, however it may differ from it in name. [Pope Leo XIII, Immortale Dei, 1885]
Laodicean: "lukewarm in religion," 1560s, from Laodicea, Syrian city (modern Latakia) whose early Christians were chastised in the Bible for indifference to their religion [Rev. iii:14-16]. The city is said to be named for the 3c B.C.E. Syrian queen Laodice, wife of Antiochus II.
revealed (adj.): 1560s, past participle adjective from reveal. Revealed religion, as opposed to natural religion, is attested from 1719.
superstitious (adj.): late 14c., "involving faith in supernatural powers or magic; characteristic of pagan religion or false religion," from Anglo-French supersticius, Old French supersticios, or directly from Latin superstitiosus "prophetic; full of dread of the supernatural," from superstitio "prophecy, soothsaying, excessive fear of the gods" (see superstition).
kathenotheism (n.): "a form of polytheism characteristic of the Vedic religion, in which one god at a time is considered supreme," 1865, coined in German by Max Müller from Greek kath' hena "one by one" + theism. Müller also coined henotheism (1860), from Greek henos "one," for "faith in a single god" as distinguished from exclusive belief in only one god, in writings on early Hebrew religion.
religious (adj.): c. 1200, "devout, pious, imbued with or expressive of religious devotion," from Anglo-French religius, Old French religious (12c., Modern French religieux) and directly from Latin religiosus, from religio (see religion). Meaning "pertaining to religion" is from 1530s. Transferred sense of "scrupulous, exact" is recorded from 1590s. Related: Religiousness.
Manichaeism (n.): 1550s, "the religion of the Manichees" (late 14c.) a Gnostic Christian sect named for its founder, Mani (Latin Manichæus), c.215-275, Syriac-speaking apostle from a Jesus cult in Mesopotamia in 240s, who taught a universal religion. Vegetarian and visionary, they saw "particles of light and goodness" trapped in evil matter and regarded Satan as co-eternal with God. The universe was a scene of struggle between good and evil. The sect was characterized by dualism and a double-standard of perfectionist "elects" and a larger group of fellow travelers who would require several reincarnations before their particles of light would be liberated.
santeria (n.): Afro-Cuban religion, 1950, from Spanish, literally "holiness, sanctity."
Islam (n.): "religious system revealed by Muhammad," 1818, from Arabic islam, literally "submission" (to the will of God), from root of aslama "he resigned, he surrendered, he submitted," causative conjunction of salima "he was safe," and related to salam "peace."
... Islam is the only major religion, along with Buddhism (if we consider the name of the religion to come from Budd, the Divine Intellect, and not the Buddha), whose name is not related to a person or ethnic group, but to the central idea of the religion. ["The Heart of Islam: Enduring Values for Humanity," Seyyed Hossein Nasr, 2002]
Earlier English names for the faith include Mahometry (late 15c.), Muhammadism (1610s), Islamism (1747), and Ismaelism (c. 1600), which in part is from Ishmaelite, a name formerly given (especially by Jews) to Arabs, as descendants of Ishmael (q.v.), and in part from Arabic Ismailiy, name of the Shiite sect that after 765 C.E. followed the Imamship through descendants of Ismail (Arabic for Ishmael), eldest son of Jafar, the sixth Imam. The Ismailians were not numerous, but among them were the powerful Fatimid dynasty in Egypt and the Assassins, both of whom loomed large in European imagination.
believer (n.): "one who has faith in religion," 1540s, agent noun from believe.
sect (n.): mid-14c., "distinctive system of beliefs or observances; party or school within a religion," from Old French secte, sete "sect, religious community," or directly from Late Latin secta "religious group, sect in philosophy or religion," from Latin secta "manner, mode, following, school of thought," literally "a way, road, beaten path," from fem. of sectus, variant past participle of sequi "follow," from PIE *sekw- (1) "to follow" (see sequel). Confused in this sense with Latin secta, fem. past participle of secare "to cut" (see section (n.)). Meaning "separately organized religious body" is recorded from 1570s.
toleration (n.): 1510s, "permission granted by authority, license," from Middle French tolération (15c.), from Latin tolerationem (nominative toleratio) "a bearing, supporting, enduring," noun of action from past participle stem of tolerare "to endure, sustain, support, suffer," literally "to bear," from PIE *tele- "to bear, carry" (see extol).

Meaning "forbearance, sufferance" is from 1580s. The specific religious sense is from 1609; as in Act of Toleration (1689), statute granting freedom of religious worship (with conditions) to dissenting Protestants in England. In this it means "recognition of the right of private judgment in matters of faith and worship; liberty granted by the government to preach and worship as one pleases; equality under the law without regard to religion."
If any man err from the right way, it is his own misfortune, no injury to thee; nor therefore art thou to punish him in the things of this life because thou supposest he will be miserable in that which is to come. Nobody, therefore, in fine, neither single persons nor churches, nay, nor even commonwealths, have any just title to invade the civil rights and worldly goods of each other upon pretence of religion. [John Locke, "Letter Concerning Toleration," 1689]

Before any man can be considered as a member of Civil Society, he must be considered as a subject of the Governour of the Universe: And if a member of Civil Society, do it with a saving of his allegiance to the Universal Sovereign. We maintain therefore that in matters of Religion, no man's right is abridged by the institution of Civil Society and that Religion is wholly exempt from its cognizance. [James Madison, "Memorial and Remonstrance Against Religious Assessments," 1785]

Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them. [Karl Popper, "The Open Society and Its Enemies," 1962]
big-tent (adj.): in reference to welcoming all sorts and not being ideologically narrow, American English, 1982 with reference to religion, by 1987 with reference to politics.
Wicca (n.): An Old English masc. noun meaning "male witch, wizard, soothsayer, sorcerer, astrologer, magician;" see witch. Use of the word in modern contexts traces to English folklorist Gerald Gardner (1884-1964), who is said to have joined circa 1939 an occult group in New Forest, Hampshire, England, for which he claimed an unbroken tradition to medieval times. Gardner seems to have first used it in print in 1954, in his book "Witchcraft Today" ("Witches were the Wica or wise people, with herbal knowledge and a working occult teaching usually used for good ...."). In published and unpublished material, he apparently only ever used the word as a mass noun referring to adherents of the practice and not as the name of the practice itself. Some of his followers continue to use it in this sense. According to Gardner's book "The Meaning of Witchcraft" (1959), the word, as used in the initiation ceremony, played a key role in his experience:
I realised that I had stumbled upon something interesting; but I was half-initiated before the word, 'Wica' which they used hit me like a thunderbolt, and I knew where I was, and that the Old Religion still existed. And so I found myself in the Circle, and there took the usual oath of secrecy, which bound me not to reveal certain things.
In the late 1960s the term came into use as the title of a modern pagan movement associated with witchcraft. The first printed reference in this usage seems to be 1969, in "The Truth About Witchcraft" by freelance author Hans Holzer:
If the practice of the Old Religion, which is also called Wicca (Craft of the Wise), and thence, witchcraft, is a reputable and useful cult, then it is worthy of public interest.
And, quoting witch Alex Sanders:
"No, a witch wedding still needs a civil ceremony to make it legal. Wicca itself as a religion is not registered yet. But it is about time somebody registered it, I think. I've done all I can to call attention to our religion."
Sanders was a highly visible representative of neo-pagan Witchcraft in the late 1960s and early 1970s. During this time he appears to have popularized use of the term in this sense. Later books c. 1989 teaching modernized witchcraft using the same term account for its rise and popularity, especially in U.S.
Bel: heaven-and-earth god of Babylonian religion, from Akkadian Belu, literally "lord, owner, master," cognate with Hebrew ba'al.
hickscorner (n.): "libertine scoffer at religion and the religious," c. 1530, from the name of the character in a work of that name printed c. 1512 by Wynkyn de Worde; from Hick, the common masc. nickname, + scorner.
autotheism (n.): "self-deification," 1610s, from auto- + theism. The religion of one who mistakes his own inner voices for God's voice in him. Also used in a theological sense (1580s) for "the regarding of the second person of the Trinity as God entire." Related: Autotheist.
skepticism (n.): also scepticism, 1640s, from skeptic + -ism. Specifically regarding Christian religion, from 1800.
secularist (n.): 1846, "one who theoretically rejects and ignores all forms of religion based on revelation;" see secularism + -ist. From 1851 as "one who maintains that public education and civil policy should be conducted without the introduction of a religious element." Related: Secularistic.
Anubis: jackal-headed god of Egyptian religion, from Greek Anoubis, from Egyptian Anpu.
unbeliever (n.): "one who does not believe in any given religion," 1520s, from un- (1) "not" believer. Old English had ungelifend in this sense.
giaour (n.): 1560s, Turkish term of contempt for non-Muslims, from Turkish pronunciation of Persian gaur, variant of gabr "infidel, fire-worshipper," originally applied to the adherents of the Zoroastrian religion. Used by the Turks especially of Christians, "and so commonly that it does not necessarily imply an insult" [Century Dictionary].
Mozarab (n.): "assimilated Christian in Moorish Spain," one who was allowed to continue practicing his religion in exchange for political allegiance, from Spanish Mozarabe "would-be Arab," from Arabic mostarib, from a desiderative verbal form of Arab.
Dracula (n.): the vampire from in Bram Stoker's novel (1897). It was a surname of Prince Vlad II of Wallachia (d.1476), and means in Romanian "son of Dracul," literally "the dragon," from the name and emblem taken by Vlad's father, also named Vlad, c. 1431 when he joined the Order of the Dragon, founded 1418 by Sigismund the Glorious of Hungary to defend the Christian religion from the Turks and crush heretics and schismatics.
conformist (n.): "one who conforms" in any way, originally usually with reference to religion; 1630s, from conform + -ist. Compare conformism.
siddha (n.): in Indian religion, "one who has attained perfection and bliss," 1846, from Sanskrit siddhah "accomplished, achieved, successful, possessing supernatural power, sorcerer, saint," related to sidhyati "reaches his goal, succeeds," sadhuh "right, skilled, excellent, a holy man."
Aesir (n.): chief gods of Scandinavian religion, from Old Norse plural of ass "god," related to Old English os, Gothic ans "god" (see Asgard).
unbias (v.): "to free from bias," 1708, from un- (2) "reverse, opposite of" + bias (v.).
The truest service a private man may hope to do his country is, by unbiassing his mind as much as possible. [Swift, "The Sentiments of a Church of England Man with respect to Religion and Government," 1708]
conformism (n.): 1890, "tendency or need to conform" to some group standard, from conform + -ism. In religion, from c. 1902. In geology from c. 1912. Modern, general sociological sense (social conformism) popularized from c. 1948.
Baha'i: 1889, mystical, tolerant Iranian religion founded by a Mirza Ali Mohammed ibn Radhik, Shiraz merchant executed for heresy in 1850, and named for his leading disciple, Baha Allah (Persian "splendor of God;" ultimately from Arabic). It also is sometimes called Babism, after the name taken by the founder, Bab-ed-Din, "gate of the faith."
apostasy (n.): late 14c., "renunciation, abandonment or neglect of established religion," from Latin apostasia, from later Greek apostasia, from apostasis "revolt, defection," literally "a standing off" (see apostate). General (non-religious) sense is attested from 1570s.
Eblis: prince of the fallen angels in Arabic mythology and religion, from Arabic Iblis. Klein thinks this may be Greek diablos, passed through Syriac where the first syllable was mistaken for the Syriac genitive particle di and dropped. "Before his fall he was called Azazel or Hharis" [Century Dictionary].
Brahma: 1785, from Sanskrit Brahma, nominative of Brahman, chief god of the trinity Brahma-Vishnu-Siva in post-Vedic Hindu religion (see brahmin).
voluntarism (n.): 1838, "theory or principal of using voluntary action rather than coercion (in politics, religion, etc.), from voluntary + -ism. (Voluntaryism in the religious sense, as opposed to establishmentarianism, is recorded from 1835.) In philosophy, "theory that the will is the basic principle," 1896, from German Voluntarismus (Tönnies, 1883).
enthusiastic (adj.): c. 1600, "pertaining to possession by a deity," from Greek enthousiastikos "inspired," from enthousiazein "be possessed or inspired by a god" (see enthusiasm). Meaning "pertaining to irrational delusion in religion" is from 1690s. The main modern sense, in reference to feelings or persons, "intensely eager, rapturous," is from 1786. Related: Enthusiastically.
Manes (pl.): "Gods of the Lower World," in Roman religion, from Latin manes "departed spirit, ghost, shade of the dead, deified spirits of the underworld," usually said to be from Latin manus "good," thus properly "the good gods," a euphemistic word, but Tucker suggests a possible connection instead to macer, thus "the thin or unsubstantial ones."
theocrat (n.): 1827, "a ruler in the name of God," from Greek theos "god" (see theo-) + -crat, from aristocrat, etc. From 1843 as "one who favors a system of theocracy." Theocratist was the name of a publication begun in 1828 "to maintain the essential relation which subsists between religion and politics," and might be used in the sense "one who emphasizes divine authority over reason and individual freedom and who explains social order as a revelation from God."
infidelity (n.): c. 1400, "want of faith, unbelief in religion; false belief, paganism;" also (early 15c.) "unfaithfulness or disloyalty to a person" (originally to a sovereign, by 16c. to a lover or spouse), from French infidélité, from Latin infidelitatem (nominative infidelitas) "unfaithfulness, faithlessness," noun of quality from infidelis (see infidel).
holiness (n.): Old English halignis "holiness, sanctity, religion; holy thing;" see holy + -ness. Compare Old High German heilagnissa. As title of the Pope, it translates Latin sanctitas (until c. 600 also applied to bishops).
Mormon (n.): 1830, coined by religion founder Joseph Smith (1805-1844) in Seneca County, N.Y., from Mormon, supposed prophet and author of "The Book of Mormon," explained by Smith as meaning more mon, from English more + Egyptian mon "good." As an adjective by 1842. Related: Mormonism.
conversion (n.): mid-14c., originally of religion, from French conversion, from Latin conversionem (nominative conversatio), noun of action from past participle stem of convertere (see convert (v.)). General sense of "transformation" is early 15c. Of buildings, from 1921. Conversion disorder "hysteria" (attested from 1946 but said to have been coined by Freud) was in DSM-IV (1994).
Christendom (n.): Old English cristendom "Christianity, state of being a Christian," from cristen (see Christian) + -dom, suffix of condition or quality. The native formation, crowded out by Latinate Christianity except for sense "lands where Christianity is the dominant religion" (late 14c.). Similar formations in Scandinavian languages.
henotheism (n.): "devotion to a single god without asserting that he or she is the only god," 1860, from Greek henos, neuter of heis "one" (from PIE *sem- (1) "one, as one;" see same) + theism. Coined by (Friedrich) Max Müller (1823-1900), professor of comparative philology at Oxford. Supposedly a characteristic of the oldest Hindu religion; or a system between monotheism and polytheism. Related: Henotheist; henotheistic.
goddess (n.): mid-14c., female deity in a polytheistic religion, from god + fem. suffix -esse (see -ess). The Old English word was gyden, corresponding to Dutch godin, German Göttin, Danish gudine, Swedish gudinna. Of mortal women by 1570s. Related: Goddesshood.
Rastafarian (n.): 1955 (Rastafarite is found from 1953), from Rastafari, Jamaican religion built around writings of Marcus Garvey and belief that Haile Selassie (1892-1975), former emperor of Ethiopia, was God. From Ras Tafari, Selassie's title from 1916 to his accession in 1936, from Amharic ras "chief, head" (from Arabic ra's) + tafari "to be feared." As an adjective from 1960.
irreligion (n.): 1590s, from Late Latin irreligionem (nominative irreligio) "irreligion, impiety," from assimiliated form of in- "not" (see in- (1)) + religio (see religion).
confession (n.): late 14c., "action of confessing," originally in religion, from Old French confession (10c.), from Latin confessionem (nominative confessio) "confession, acknowledgement," noun of action from past participle stem of confiteri (see confess). In law, from 1570s. Meaning "that which is confessed" is mid-15c. An Old English word for it was andettung, also scriftspræc.
mufti (n.): 1580s, muphtie "official head of the state religion in Turkey," from Arabic mufti "judge," active participle of afta "to give," conjugated form of fata "he gave a (legal) decision" (compare fatwa). Sense of "ordinary clothes (not in uniform)" is from 1816, of unknown origin, perhaps from mufti's costume of robes and slippers in stage plays, which was felt to resemble plain clothes.
ministerial (adj.): 1560s, of religion; 1650s, of state; in some uses from Middle French ministériel and directly from Medieval Latin ministerialis "pertaining to service, of a minister," from Latin ministerium (see ministry); in some cases probably directly from minister or ministry.
apostate (n.): mid-14c., "one who forsakes his religion or faith," from Old French apostate (Modern French apostat) and directly from Late Latin apostata, from Greek apostasia "defection, desertion, rebellion," from apostenai "to defect," literally "to stand off," from apo- "away from" (see apo-) + stenai "to stand." Used in non-religious situations (politics, etc.) from mid-14c.