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 (12c.) or directly from Latin infidelitatem (nominative infidelitas) "unfaithfulness, faithlessness," noun of quality from infidelis "unfaithful, unbelieving" (see infidel).
"person of limited or feeble intelligence," 1640s, according to OED probably a jocular formation from simple and -ton, suffix extracted from surnames (and ultimately place-names). Compare skimmington, personification of an ill-used spouse, c. 1600; OED compares idleton from the English Dialect Dictionary. Century Dictionary sees it as a French diminutive of simplet, though no such diminutive had yet turned up. Also compare the -by terminations under rudesby.
"act of conniving, an overlooking of a disreputable or illegal action, often implying private approval," especially, in divorce law, "corrupt consent of a married person to that conduct of the spouse of which complaint is later made," 1590s, from French connivence or directly from Latin conniventia, from conniventem (nominative connivens), present participle of connivere "to wink," hence, "to wink at (a crime), be secretly privy" (see connive). According to OED, the spelling with -a- prevailed after early 18c. but is unetymological.
mid-15c., "to take as spouse, marry," from Old French espouser "marry, take in marriage, join in marriage" (11c., Modern French épouser), from Latin sponsare, past participle of spondere "make an offering, perform a rite, promise secretly," hence "to engage oneself by ritual act" (see sponsor (n.)). Extended sense of "adopt, embrace" a cause, party, etc., is from 1620s. Related: Espoused; espouses; espousing. For initial e-, see e-.
Earth as a goddess, from Greek Gaia, spouse of Uranus, mother of the Titans, personification of gaia "earth" (as opposed to heaven), "land" (as opposed to sea), "a land, country, soil;" it is a collateral form of gē (Dorian ga) "earth," which is of unknown origin and perhaps from a pre-Indo-European language of Greece. The Roman equivalent goddess of the earth was Tellus (see tellurian), sometimes used in English poetically or rhetorically for "Earth personified" or "the Earth as a planet."
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.
early 14c., "sincerely religious, devout, pious," especially in reference to Christian practice; mid-14c., "loyal (to a lord, friend, spouse, etc.); true; honest, trustworthy," from faith + -ful. From late 14c. in reference to a tale, a report, etc., "accurate, reliable, true to the facts." The noun sense of "true believer, one who is full of faith" is from late 14c. (Church Latin used fideles in same sense). Related: Faithfully; faithfulness. Old Faithful geyser named 1870 by explorer Gen. Henry Dana Washburn, surveyor-general of the Montana Territory, in reference to the regularity of its outbursts.
Old English gadrian, gædrian "unite, agree, assemble; gather, collect, store up" (transitive and intransitive), used of flowers, thoughts, persons; from Proto-Germanic *gaduron "come or bring together, unite" (source also of Old English gæd "fellowship, companionship," gædeling "companion;" Middle Low German gadderen; Old Frisian gaderia; Dutch gaderen "to gather," gade "spouse;" German Gatte "husband;" Gothic gadiliggs), perhaps from PIE *ghedh- "to unite, join" (see good (adj.)). Change of spelling from -d- to -th- is 1500s, reflecting earlier change in pronunciation (as in father). Related: Gathered; gathering.
1894, "anyone of a relationship not natural," abstracted from father-in-law, etc.
The position of the 'in-laws' (a happy phrase which is attributed ... to her Majesty, than whom no one can be better acquainted with the article) is often not very apt to promote happiness. [Blackwood's Magazine, 1894]
The earliest recorded use of the formation is in brother-in-law (13c.); the law is Canon Law, which defines degrees of relationship within which marriage is prohibited. Thus the word originally had a more narrow application; its general extension to more distant relatives of one's spouse is, according to OED "recent colloquial or journalistic phraseology." Middle English inlaue (13c.) meant "one within or restored to the protection and benefit of the law" (opposite of an outlaw), from a verb inlauen, from Old English inlagian "reverse sentence of outlawry."