Etymology
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atheism (n.)

"the doctrine that there is no God;" "disbelief in any regularity in the universe to which man must conform himself under penalties" [J.R. Seeley, "Natural Religion," 1882], 1580s, from French athéisme (16c.), with -ism + Greek atheos "without a god, denying the gods," from a- "without" (see a- (3)) + theos "a god" (from PIE root *dhes-, forming words for religious concepts). A slightly earlier form is represented by atheonism (1530s) which is perhaps from Italian atheo "atheist." The ancient Greek noun was atheotes "ungodliness."

In late 19c. sometimes further distinguished into secondary senses "The denial of theism, that is, of the doctrine that the great first cause is a supreme, intelligent, righteous person" [Century Dictionary, 1897] and "practical indifference to and disregard of God, godlessness."

In the first sense above given, atheism is to be discriminated from pantheism, which denies the personality of God, and from agnosticism, which denies the possibility of positive knowledge concerning him. In the second sense, atheism includes both pantheism and agnosticism. [Century Dictionary]
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theism (n.)

1670s, "belief in a deity or deities," (as opposed to atheism); by 1711 as "belief in one god" (as opposed to polytheism); by 1714 as "belief in the existence of God as creator and ruler of the universe" (as opposed to deism), the usual modern sense; see theist + -ism.

Theism assumes a living relation of God to his creatures, but does not define it. It differs from deism in that the latter is negative and involves a denial of revelation, while the former is affirmative, and underlies Christianity. One may be a theist and not be a Christian, but he cannot be a Christian and not be a theist. [Century Dictionary]
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deism (n.)

"belief in the existence of a personal God, generally accompanied by denial of revelation and the authority of a church," 1680s (deist is from 1620s), from French déisme, from Latin deus "god," from PIE root *dyeu- "to shine," in derivatives "sky, heaven, god."

A type of rationalistic theology that rose to prominence in England in the late 17c. and early 18c.; the deists advocated for the sufficiency of natural religion, apart from Scripture or revelation. Until c. 1700, the word was opposed to atheism; later it was the opposite of theism (q.v.), with which it is etymologically equivalent.

The term "deism" not only is used to signify the main body of the deists' teaching, or the tendency they represent, but has come into use as a technical term for one specific metaphysical doctrine as to the relation of God to the universe, assumed to have been characteristic of the deists, and to have distinguished them from atheists, pantheists and theists,—the belief, namely, that the first cause of the universe is a personal God, who is, however, not only distinct from the world but apart from it and its concerns. [Encyclopaedia Britannica, 1922]
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*dhes- 
*dhēs-, Proto-Indo-European root forming words for religious concepts. Possibly an extension of PIE root *dhe- "to set, put."

It forms all or part of: apotheosis; atheism; atheous; Dorothy; enthusiasm; fair (n.) "a stated market in a town or city;" fanatic; ferial; feast; fedora; -fest; festal; festival; festive; festoon; Festus; fete; fiesta; henotheism; monotheism; pantheism; pantheon; polytheism; profane; profanity; Thea; -theism; theist; theo-; theocracy; theodicy; Theodore; Theodosia; theogony; theology; theophany; Theophilus; theosophy; theurgy; tiffany; Timothy.

It is the hypothetical source of/evidence for its existence is provided by: Greek theos "god;" Latin feriae "holidays," festus "festive," fanum "temple."
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atheistic (adj.)
"involving or characteristic of atheism," 1630s, from atheist + -ic. Atheistical attested from 1580s. Milton used atheous in this sense. Related: Atheistically.
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determinism (n.)

1846, introduced by William Hamilton for "doctrine of the necessitarian philosophers" (who hold that human action is not free but necessarily determined by motives, regarded as external forces acting on the will or character of the person). See determine + -ism.

Determinism does not imply materialism, atheism, or a denial of moral responsibility; while it is in direct opposition to fatalism and to the doctrine of the freedom of the will. [Century Dictionary]

 From 1876 in general sense of "doctrine that everything happens is determined by a necessary chain of causation," from French déterminisme, from German Determinismus, perhaps a back-formation from Praedeterminismus.

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