Etymology
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fealty (n.)
c. 1300, feaute, from Old French feauté, earlier fealte, "loyalty, fidelity; homage sworn by a vassal to his overlord; faithfulness," from Latin fidelitatem (nominative fidelitas) "faithfulness, fidelity," from fidelis "loyal, faithful" (from PIE root *bheidh- "to trust, confide, persuade").
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federation (n.)

1721, "union by agreement," from French fédération, from Late Latin foederationem (nominative foederatio), noun of action from past-participle stem of Latin foederare "league together," from foedus "covenant, league" (from PIE root *bheidh- "to trust, confide, persuade").

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affidavit (n.)
"written declaration upon an oath," 1590s, from Medieval Latin affidavit, literally "he has stated on oath," third person singular perfective of affidare "to trust; to make an oath," from Latin ad "to" (see ad-) + fidare "to trust," from fidus "faithful," from PIE root *bheidh- "to trust, confide, persuade." So called from being the first word of sworn statements.
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federate (v.)
1814 (implied in federated), a back-formation from federation, or else from Latin foederatus "leagued, federated, combined; having a treaty, bound by treaty," past participle of foederare "to establish by treaty," from foedus "covenant, treaty, alliance" (from PIE root *bheidh- "to trust, confide, persuade"). Related: Federating. As an adjective, by 1710.
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defiance (n.)
Origin and meaning of defiance

c. 1300, defiaunce, "a challenge to fight, invitation to combat," from Old French desfiance "challenge, declaration of war," from desfiant, present participle of 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 PIE root *bheidh- "to trust, confide, persuade"). By 1710 as "contempt of opposition or danger."

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teach (v.)

Old English tæcan (past tense tæhte, past participle tæht) "to show, point out, declare, demonstrate," also "to give instruction, train, assign, direct; warn; persuade," from Proto-Germanic *taikijan "to show" (source also of Old High German zihan, German zeihen "to accuse," Gothic ga-teihan "to announce"), from PIE root *deik- "to show, point out." Related to Old English tacen, tacn "sign, mark" (see token). Related: Taught; teaching.

Lemonade Vendor (Edgar Kennedy), enraged: I'll teach you to kick me!
Chico: you don't have to teach me, I know how. [kicks him]

The usual sense of Old English tæcan was "show, declare, warn, persuade" (compare German zeigen "to show," from the same root); while the Old English word for "to teach, instruct, guide" was more commonly læran, source of modern learn and lore.

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confident (adj.)

1570s, "self-reliant, sure of oneself;" c. 1600, "fully assured, having strong belief," from French confident, from Latin confidentem (nominative confidens) "firmly trusting, reliant, self-confident, bold, daring," present participle of confidere "to have full trust or reliance," from assimilated form of com, here perhaps an intensive prefix (see com-), + fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). Related: Confidently.

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dissuade (v.)

1510s, from French dissuader and directly from Latin 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: Dissuaded; dissuading.

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*bheidh- 
Proto-Indo-European root meaning "to trust, confide, persuade."

It forms all or part of: abide; abode; affiance; affidavit; auto-da-fe; bide; bona fide; confederate; confidant; confide; confidence; confident; defiance; defy; diffidence; diffident; faith; fealty; federal; federate; federation; fiancee; fideism; fidelity; fiducial; fiduciary; infidel; infidelity; nullifidian; perfidy; solifidian.

It is the hypothetical source of/evidence for its existence is provided by: Greek pistis "faith, confidence, honesty;" Latin fides "trust, faith, confidence, reliance, credence, belief;" Albanian be "oath," bindem "to be convinced, believe;" Old Church Slavonic beda "distress, necessity," bediti "to force, persuade;" Old English biddan "to ask, beg, pray," German bitten "to ask."
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solifidian (n.)
"one who believes in salvation by faith alone" (based on Luther's translation of Romans iii.28), 1590s, Reformation coinage from Latin solus "alone" (see sole (adj.)) + fides "faith" (from PIE root *bheidh- "to trust, confide, persuade"). As an adjective from c. 1600. Related: Solifidianism
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