Etymology
Advertisement
fidelity (n.)

early 15c., "faithfulness, devotion," from Old French fidélité (15c.), from Latin fidelitatem (nominative fidelitas) "faithfulness, adherence, trustiness," from fidelis "faithful, true, trusty, sincere," from fides "faith" (from PIE root *bheidh- "to trust, confide, persuade"). From 1530s as "faithful adherence to truth or reality;" specifically of sound reproduction from 1878.

Related entries & more 
Advertisement
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" (from PIE root *bheidh- "to trust, confide, persuade"). It has all but expelled native betrothed. The English verb fiance, now obsolete, was used c. 1450-1600 for "to engage to be married."
Related entries & more 
confide (v.)

mid-15c., "to place trust or have faith," from Latin confidere "to trust in, rely firmly upon, believe," from assimilated form of com, here perhaps an intensive prefix (see com-), + fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). Meaning "to share a secret with, take into one's confidence" is from 1735; phrase confide in (someone) is from 1888. Related: Confided; confiding.

Related entries & more 
diffident (adj.)
Origin and meaning of diffident

mid-15c., "distrustful, wanting confidence in another's power," from Latin diffidentem (nominative diffidens), present participle of diffidere "to mistrust, lack confidence," from dis- "away" (see dis-) + fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). Original sense is obsolete; modern sense of "distrustful of oneself, not confident" is by 1713. Compare diffidence. Related: Diffidently.

Related entries & more 
suasion (n.)
late 14c., from Old French suasion (14c.) and directly from Latin suasionem (nominative suasio) "a recommending, advocacy, support," noun of action from past participle stem of suadere "to urge, incite, promote, advise, persuade," literally "recommend as good" (related to suavis "sweet"), from PIE root *swād- "sweet, pleasant" (see sweet (adj.)). Survives chiefly in phrase moral suasion (1640s). Latin Suada was the goddess of persuasion.
Related entries & more 
Advertisement
confidant (n.)

1610s, confident, "(male) person trusted with private affairs," from French confident (16c.), from Italian confidente "a trusty friend," literally "confident, trusty," from Latin confidentem (nominative confidens), present participle of confidere "to trust, confide," from assimilated form of com, here perhaps an intensive prefix (see com-), + fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). The spelling with -a- and the pronunciation with the stress on the last syllable came to predominate 18c. and might reflect the French pronunciation.

Related entries & more 
confederate (v.)
Origin and meaning of confederate

1530s, "to unite in a league or alliance," from Late Latin confoederatus, past participle of confoederare "to unite by a league," from assimilated form of com "with, together" (see con-) + foederare, from foedus (genitive foederis) "a league," from suffixed form of PIE root *bheidh- "to trust, confide, persuade."

The older verb was confeder (late 14c.), from Old French confederer, Medieval Latin confederare. Related: Confederated; confederating.

Related entries & more 
dissuasion (n.)

early 15c., dissuasioun, "advice or exhortation in opposition to something," from Old French dissuasion (14c.) and directly from Latin dissuasionem (nominative dissuasio) "an advice to the contrary," noun of action from past-participle stem of dissuadere "to advise against, oppose by argument," from dis- "off, against" (see dis-) + suadere "to urge, incite, promote, advise, persuade," literally "recommend as good" (related to suavis "sweet"), from PIE root *swād- "sweet, pleasant" (see sweet (adj.)).

Related entries & more 
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 PIE root *bheidh- "to trust, confide, persuade."

From mid-16c. especially "to promise in marriage." The earlier form of the word was affy (Middle English affien "to trust, have faith; have faith in" c. 1300), from Old French afier. Related: Affianced; affiancing.
Related entries & more 
auto-da-fe (n.)
"sentence passed by the Inquisition" (plural autos-da-fé), 1723, from Portuguese auto-da-fé "judicial sentence, act of the faith," especially the public burning of a heretic, from Latin actus de fide. The elements are auto "a play," in law, "an order, decree, sentence," from Latin actus (see act (v.)), de "from, of" (see de), fides "faith" (from PIE root *bheidh- "to trust, confide, persuade"). The Spanish form is auto-de-fe, but the Portuguese form took hold in English, perhaps through popular accounts of the executions following the earthquake of 1755.
Related entries & more 

Page 3