c. 1300, mariage, "action of entering into wedlock;" also "state or condition of being husband and wife, matrimony, wedlock;" also "a union of a man and woman for life by marriage, a particular matrimonial union;" from Old French mariage "marriage; dowry" (12c.), from Vulgar Latin *maritaticum (11c.), from Latin maritatus, past participle of maritare "to wed, marry, give in marriage" (see marry (v.)). The Vulgar Latin word also is the source of Italian maritaggio, Spanish maridaje, and compare mariachi.
Meanings "the marriage vow, formal declaration or contract by which two join in wedlock;" also "a wedding, the celebration of a marriage; the marriage ceremony" are from late 14c. Figurative use (non-theological) "intimate union, a joining as if by marriage" is from late 14c.
[W]hen two people are under the influence of the most violent, most insane, most delusive, and most transient of passions, they are required to swear that they will remain in that excited, abnormal, and exhausting condition until death do them part. [G.B. Shaw, preface to "Getting Married," 1908]
Marriage counseling is recorded by that name by 1939. Marriage bed, figurative of marital intercourse generally, is attested from 1580s (bed of marriage is from early 15c.).
"want of loyalty, unfaithful behavior," early 15c., disloialte, from a variant of Old French desloiaute, desleauté "disloyalty, faithlessness, marital infidelity," from desloial, desleal "treacherous, false, deceitful" (Modern French déloyal), from des- "not, opposite of" (see dis-) + loial "of good quality; faithful; honorable; law-abiding; legitimate, born in wedlock," from Latin legalem, from lex "law" (see legal). Since c. 1600 especially "violation of allegiance or duty to a state or sovereign."
"betroth (two people), bind in wedlock; pledge oneself to," early 12c., from Old English handfæsten and cognate Old Norse handfesta "to pledge, betroth; strike a bargain by shaking hands;" for first element see hand (n.); second element is from Proto-Germanic causative verb *fastjan "to make firm," from PIE *past- "solid, firm" (see fast (adj.)). Related: Handfasted; handfasting. The noun in Old English was handfæstung.
early 15c. (implied in disloyally), "not true to one's allegiance" (to a sovereign, state, or government), from Old French desloial, desleal "treacherous, false, deceitful" (Modern French déloyal), from des- "not, opposite of" (see dis-) + loial "of good quality; faithful; honorable; law-abiding; legitimate, born in wedlock," from Latin legalem, from lex "law" (see legal). Sometimes also "not true to one's obligations or engagements," especially to a lover, spouse, or friend, (late 15c.), but this sense is rare.
From late 14c. as "lightheartedness, cheerfulness." A word with more senses in Middle and early Modern English than recently: "sexual pleasure or indulgence, lust" (mid-14c.); "insolent presumptuousness, impudence" (mid-14c.); "vigor, strength" (mid-14c.); "love; a love affair" (c. 1300, hence in jollity "by fornication, out of wedlock"); "gallantry" (1530s); "state of splendor" (1540s).
"womanhood, state of puberty in a woman," corresponding to virility in men, 1590s, from Late Latin muliebritatem (nominative muliebritas) "womanhood," from Latin muliebris "of woman, womanly," from mulier "a woman," which is traditionally said to be comparative to the stem of mollis "soft, weak;" there are phonetic objections, but no better theory has come forward.
Hence also mulier, in old law language "a woman; a wife," as an adjective, "born in wedlock." Also muliebral "of or pertaining to a woman" (1650s); muliebrious "effeminate" (1650s); mulierosity "excessive fondness for women." In old anatomy and medical writing pudenda muliebria was euphemistic for "vagina."
"true or faithful in allegiance," 1530s, in reference to subjects of sovereigns or governments, from French loyal, from Old French loial, leal "of good quality; faithful; honorable; law-abiding; legitimate, born in wedlock," from Latin legalem, from lex "law" (see legal).
Identical with legal, which maintains the Latin form; in most uses it has displaced Middle English leal, which is an older borrowing of the French word. For the twinning, compare royal/regal. Sense development in English is feudal, via notion of "faithful in carrying out legal obligations; conformable to the laws of honor." In a general sense (of dogs, lovers, etc.), from c. 1600. As a noun meaning "those who are loyal" from 1530s (originally often in plural).