Online Etymology Dictionary

faith (n.): mid-13c., faith, feith, fei, fai "faithfulness to a trust or promise; loyalty to a person; honesty, truthfulness," from Anglo-French and Old French feid, foi "faith, belief, trust, confidence; pledge" (11c.), from Latin fides "trust, faith, confidence, reliance, credence, belief," from root of fidere "to trust," from PIE root *bheidh- "to trust" (source also of Greek pistis "faith, confidence, honesty;" see bid). For sense evolution, see belief. Accomodated to other English abstract nouns in -th (truth, health, etc.).

From early 14c. as "assent of the mind to the truth of a statement for which there is incomplete evidence," especially "belief in religious matters" (matched with hope and charity). Since mid-14c. in reference to the Christian church or religion; from late 14c. in reference to any religious persuasion.
And faith is neither the submission of the reason, nor is it the acceptance, simply and absolutely upon testimony, of what reason cannot reach. Faith is: the being able to cleave to a power of goodness appealing to our higher and real self, not to our lower and apparent self. [Matthew Arnold, "Literature & Dogma," 1873]
From late 14c. as "confidence in a person or thing with reference to truthfulness or reliability," also "fidelity of one spouse to another." Also in Middle English "a sworn oath," hence its frequent use in Middle English oaths and asseverations (par ma fay, mid-13c.; bi my fay, c. 1300).
faith-healer (n.): Also faith healer, attested by 1874; from faith + healer. Faith-curer is from 1883.
The power which a man's imagination has over his body to heal it or make it sick is a force which none of us is born without. The first man had it, the last one will possess it. If left to himself, a man is most likely to use only the mischievous half of the force--the half which invents imaginary ailments for him and cultivates them; and if he is one of those very wise people, he is quite likely to scoff at the beneficent half of the force and deny its existence. [Mark Twain, "Christian Science," 1907]
faithless (adj.): c. 1300, "unbelieving," from faith + -less. Meaning "insincere, deceptive" is mid-14c. Related: Faithlessly; faithlessness.
faithful (adj.): 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 (1832-1871), surveyor-general of the Montana Territory, in reference to the regularity of its outbursts.
bona fide: 1540s, Latin, literally "in good faith," ablative of bona fides "good faith" (see faith). Originally used as an adverb, later (18c.) also as an adjective. The opposite is mala fide.
fidelity (n.): early 15c., "faithfulness, devotion," from Middle French fidélité (15c.), from Latin fidelitatem (nominative fidelitas) "faithfulness, adherence, trustiness," from fidelis "faithful, true, trusty, sincere," from fides "faith" (see faith). From 1530s as "faithful adherence to truth or reality;" specifically of sound reproduction from 1878.
fiducial (adj.): 1570s, "assumed as a fixed basis for comparison," from Latin fiducialis "reliable," from fiducia "trust" (see faith). From 1620s as "pertaining to trust;" 1832 as "fiduciary."
federal (adj.): 1640s, as a theological term (in reference to "covenants" between God and man), from French fédéral, an adjective formed from Latin foedus (genitive foederis) "covenant, league, treaty, alliance," from PIE *bhoid-es-, from root *bheidh- "to trust" (which also is the source of Latin fides "faith;" see faith).

Secular meaning "pertaining to a covenant or treaty" (1650s) led to political sense of "formed by agreement among independent states" (1707), from use of the word in federal union "union based on a treaty" (popularized during formation of U.S.A. 1776-1787) and like phrases. Also from this period in U.S. history comes the sense "favoring the central government" (1788) and the especial use of the word (as opposed to confederate) to mean a state in which the federal authority is independent of the component parts within its legitimate sphere of action. Used from 1861 in reference to the Northern forces in the American Civil War.
fiduciary (adj.): 1640s, "holding something in trust," from Latin fiduciarius "entrusted, held in trust," from fiducia "trust, confidence, reliance;" in law, "a deposit, pledge, security," from root of fidere "to trust" (see faith). In Roman law, fiducia was "a right transferred in trust;" paper currency sense (1878) is because its value depends on the trust of the public. As a noun, "one who holds something in trust," from 1630s.
interfaith (adj.): 1921, from inter- + faith.
fideism (n.): in various theological doctrines making knowledge dependent on faith, 1885, from Latin fides "faith" (see faith) + -ism.
nullifidian (n.): 1560s, from Latin nulli-, comb. form of nullus "no" (see null) + fides "faith" (see faith).
solifidian (n.): "one who believes in salvation by faith alone" (based on Luther's translation of Rom. iii:28), 1590s, Reformation coinage from Latin solus "alone" (see sole (adj.)) + fides "faith" (see faith). As an adjective from c. 1600. Related: Solifidianism
affidavit (n.): 1590s, from Medieval Latin affidavit, literally "he has stated on oath," third person singular perfective of affidare "to trust," from Latin ad- "to" (see ad-) + fidare "to trust," from fidus "faithful," from the same root as fides "faith" (see faith). So called from being the first word of sworn statements.
defy (v.): c. 1300, "to renounce one's allegiance;" mid-14c., "to challenge, defy," from Old French defier, desfier "to challenge, defy, provoke; renounce (a belief), repudiate (a vow, etc.)," from Vulgar Latin *disfidare "renounce one's faith," from Latin dis- "away" (see dis-) + fidus "faithful," from the same root as fides "faith" (see faith).
fiancee (n.): "woman to whom one is betrothed," 1844 (1837 as a French word in English), from French fiancée, fem. of fiancé, past participle of fiancer "to betroth," from fiance "a promise, trust," from fier "to trust," from Vulgar Latin *fidare "to trust," from Latin fidus "faithful" from the same root as fides "faith" (see faith). It has all but expelled native betrothed. The English verb fiance, now obsolete, was used c. 1450-1600 for "to engage to be married."
perfidy (n.): 1590s, from Middle French perfidie (16c.), from Latin perfidia "faithlessness, falsehood, treachery," from perfidus "faithless," from phrase per fidem decipere "to deceive through trustingness," from per "through" (see per) + fidem (nominative fides) "faith" (see faith).
[C]ombinations of wickedness would overwhelm the world by the advantage which licentious principles afford, did not those who have long practiced perfidy grow faithless to each other. [Samuel Johnson, "Life of Waller"]
affiance (v.): 1520s, "to promise," from Old French afiancier "to pledge, promise, give one's word," from afiance (n.) "confidence, trust," from afier "to trust," from Late Latin affidare, from ad- "to" (see ad-) + fidare "to trust," from fidus "faithful" from the same root as fides "faith" (see faith). From mid-16c. especially "to promise in marriage." Related: Affianced; affiancing.
diffidence (n.): c. 1400, from Latin diffidentia "mistrust, distrust, want of confidence," from diffidere "to mistrust, lack confidence," from dis- "away" (see dis-) + fidere "to trust" (see faith). Modern sense is of "distrusting oneself" (1650s). The original sense was the opposite of confidence.
confidence (n.): early 15c., from Middle French confidence or directly from Latin confidentia, from confidentem (nominative confidens) "firmly trusting, bold," present participle of confidere "to have full trust or reliance," from com-, intensive prefix (see com-), + fidere "to trust" (see faith). For sense of "swindle" see con (adj.).
ovate (n.): 1723, from assumed Latin plural Ovates, from Greek Ouateis "soothsayers, prophets," mentioned by Strabo as a third order in the Gaulish hierarchy, from Proto-Celtic *vateis, plural of *vatis, cognate with Latin vatis, Old Irish faith, Welsh ofydd. The modern word, and the artificial senses attached to it, are from the 18c. Celtic revival and the word appears first in Henry Rowlands.
vates (n.): 1620s, "poet or bard," specifically "Celtic divinely inspired poet" (1728), from Latin vates "sooth-sayer, prophet, seer," from a Celtic source akin to Old Irish faith "poet," Welsh gwawd "poem," from PIE root *wet- (1) "to blow; inspire, spiritually arouse" (source also of Old English wod "mad, frenzied," god-name Woden; see wood (adj.)). Hence vaticination "oracular prediction" (c. 1600).
belief (n.): late 12c., bileave, replacing Old English geleafa "belief, faith," from West Germanic *ga-laubon "to hold dear, esteem, trust" (source also of Old Saxon gilobo, Middle Dutch gelove, Old High German giloubo, German Glaube), from *galaub- "dear, esteemed," from intensive prefix *ga- + *leubh- "to care, desire, like, love" (see love (v.)). The prefix was altered on analogy of the verb believe. The distinction of the final consonant from that of believe developed 15c.
The be-, which is not a natural prefix of nouns, was prefixed on the analogy of the vb. (where it is naturally an intensive) .... [OED]
Belief used to mean "trust in God," while faith meant "loyalty to a person based on promise or duty" (a sense preserved in keep one's faith, in good (or bad) faith and in common usage of faithful, faithless, which contain no notion of divinity). But faith, as cognate of Latin fides, took on the religious sense beginning in 14c. translations, and belief had by 16c. become limited to "mental acceptance of something as true," from the religious use in the sense of "things held to be true as a matter of religious doctrine" (a sense attested from early 13c.).
wood (adj.): "violently insane" (now obsolete), from Old English wod "mad, frenzied," from Proto-Germanic *woda- (source also of Gothic woþs "possessed, mad," Old High German wuot "mad, madness," German wut "rage, fury"), from PIE *wet- (1) "to blow; inspire, spiritually arouse;" source of Latin vates "seer, poet," Old Irish faith "poet;" "with a common element of mental excitement" [Buck]. Compare Old English woþ "sound, melody, song," Old Norse oðr "poetry," and the god-name Odin.
Edda (n.): 1771, by some identified with the name of the old woman (literally "grandmother") in the Old Norse poem "Rigsþul," by others derived from Old Norse oðr "spirit, mind, passion, song, poetry" (cognate with Old Irish faith "poet," Welsh gwawd "poem," Old English woþ "sound, melody, song," Latin vates "seer, soothsayer;" see wood (adj.)).

It is the name given in Icelandic c. 1300, by whom it is not known, to two Icelandic books, the first a miscellany of poetry, mythology, and grammar by Snorri Sturluson (d.1241), since 1642 called the Younger or Prose Edda; and a c. 1200 collection of ancient Germanic poetry and religious tales, called the Elder or Poetic Edda. Related: Eddaic; Eddic.
Catholicism (n.): "faith and practice of the Catholic church," 1610s, from Catholic + -ism.
believer (n.): "one who has faith in religion," 1540s, agent noun from believe.
Aladdin: name of a hero in stories from the Arabian Nights, from Arabic Ala' al Din, literally "nobility of faith."
Muslim (n.): 1610s, from Arabic muslim "one who submits" (to the faith), from root of aslama "he resigned." Related to Islam. From 1777 as an adjective.
bona fides (n.): by 1838, English pluralization of bona fide, as though it were a noun meaning "guarantee of good faith."
auto-da-fe (n.): 1723, "sentence passed by the Inquisition" (plural autos-da-fé), from Portuguese auto-da-fé "judicial sentence, act of the faith," especially the public burning of a heretic, from Latin actus de fide, literally "act of faith." Although the Spanish Inquisition is better-known today, there also was one in Portugal.
truce (n.): "mutually agreed-upon temporary intermission of hostilities," early 13c., triws, variant of trewes, originally plural of trewe "faith, assurance of faith, covenant, treaty," from Old English treow "faith, truth, fidelity; pledge, promise, agreement, treaty," from Proto-Germanic *treuwaz- (source also of Old Frisian triuwe, Middle Dutch trouwe, Dutch trouw, Old High German triuwa, German treue, Gothic triggwa "faith, faithfulness"). Related to Old English treowe "faithful" (see true (adj.)). The Germanic word was borrowed into Late Latin as tregua, hence French trève, Italian tregua.
Fay: fem. proper name, in some cases from Middle English fei, Old French fei "faith," or else from fay "fairy."
lapsed (adj.): of persons, "fallen away from the faith," 1630s, past participle adjective from lapse (v.). Originally especially to those who denied Christianity during prosecution.
universalism (n.): 1805 in theology, "the doctrine of universal salvation," from universal (adj.) + -ism. Universalist "one who, professing the Christian faith, believes in the eventual redemption of all humanity" is attested from 1620s.
defection (n.): 1540s, "action of failing;" 1550s, "action of deserting a party, leader, etc." from Latin defectionem (nominative defectio) "desertion, revolt, failure," noun of action from past participle stem of deficere (see deficient). Originally used often of faith.
implicit (adj.): 1590s, "implied, resting on inference," from Middle French implicite and directly from Latin implicitus, later variant of implicatus "entangled, confused, involved," past participle of implicare "entangle, involve" (see implication). From c. 1600 as "resulting from perfect confidence (in authority), unquestioning" (especially of faith).
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).
confide (v.): mid-15c., "to trust or have faith," from Latin confidere "to trust in, rely firmly upon, believe" (see confidence). Meaning "to share a secret with" is from 1735; phrase confide in (someone) is from 1888. Related: Confided; confiding.
cocoon (v.): 1986, "to stay inside and be inactive," from coccoon (n.).
A lady with an enchanting name, Faith Popcorn, has identified a menacing new American behavior that she gives the sweet name of 'cocooning.' It threatens the nation's pursuit of happiness, sometimes called the economy. [George Will, April 1987]
Related: Cocooned; cocooning.
very (adj.): late 13c., verray "true, real, genuine," later "actual, sheer" (late 14c.), from Anglo-French verrai, Old French verai "true, truthful, sincere; right, just, legal," from Vulgar Latin *veracus, from Latin verax (genitive veracis) "truthful," from verus "true" (source also of Italian vero), from PIE root *were-o- "true, trustworthy" (source also of Old English wær "a compact," Old Dutch, Old High German war, Dutch waar, German wahr "true;" Welsh gwyr, Old Irish fir "true;" Old Church Slavonic vera "faith," Russian viera "faith, belief"). Meaning "greatly, extremely" is first recorded mid-15c. Used as a pure intensive since Middle English.
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."
credo (n.): late 12c., from Latin, literally "I believe," first word of the Apostles' and Nicene Creeds, first person singular present indicative of credere "to believe," from PIE compound *kerd-dhe- "to believe," literally "to put one's heart" (source also of Old Irish cretim, Irish creidim, Welsh credu "I believe," Sanskrit śrad-dhā- "faith"), from PIE root *kerd- (1) "heart" (see heart (n.)). The nativized form is creed. General sense of "formula or statement of belief" is from 1580s.
edify (v.): mid-14c., "to build, construct," also, in figurative use, "to build up morally or in faith," from Old French edefiier (12c., Modern French édifier) "build; install; teach, instruct (morally)," from Latin aedificare "to build, construct," in Late Latin "improve spiritually, instruct" (see edifice). Related: Edified; edifying.
oblige (v.): c. 1300, "to bind by oath," from Old French obligier "engage one's faith, commit (oneself), pledge" (13c.), from Latin obligare "to bind, bind up, bandage," figuratively "put under obligation," from ob "to" (see ob-) + ligare "to bind," from PIE root *leig- "to bind" (see ligament). Main modern meaning "to make (someone) indebted by conferring a benefit or kindness" is from 1560s. Related: obliged; obliging.
putative (adj.): early 15c., from Middle French putatif, from Late Latin putativus "supposed," from Latin putat-, past participle stem of putare "to judge, suppose, believe, suspect," originally "to clean, trim, prune" (see pave). At first especially in putative marriage, one which, though legally invalid, was contracted in good faith by at least one party. Related: Putatively.
Rasputin: acquired name (Russian, literally "debauchee") of Grigory Yefimovich Novykh (c. 1872-1916), mystic and faith healer who held sway over court of Nicholas II of Russia. His nickname is from his doctrine of "rebirth through sin," that true holy communion must be preceded by immersion in sin. His name used figuratively in English from 1937 for anyone felt to have an insidious and corrupting influence.
Judaism (n.): c. 1400 (attested in Anglo-Latin from mid-13c.), from Old French Judaisme and directly from Late Latin Judaismus, from Greek Ioudaismos, from Ioudaios "Jew" (see Jew). The Anglo-Latin reference is from a special tax levied on the Jews of England. Earlier in same sense was Juhede "Jewish faith, Judaism," literally "Jew-hood" (early 14c.).
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 (12c.) or directly from Latin infidelitatem (nominative infidelitas) "unfaithfulness, faithlessness," noun of quality from infidelis "unfaithful, unbelieving" (see infidel).
testify (v.): late 14c., "give legal testimony, affirm the truth of, bear witness to;" of things, c. 1400, "serve as evidence of," from Anglo-French testifier, from Latin testificari "bear witness, show, demonstrate," also "call to witness," from testis "a witness" (see testament) + root of facere "to make" (see factitious). Biblical sense of "openly profess one's faith and devotion" is attested from 1520s. Related: Testified; testifying; testification.