Etymology
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perfidy (n.)

"breach of faith or trust, base treachery," 1590s, from French perfidie (16c.), from Latin perfidia "faithlessness, falsehood, treachery," from perfidus "faithless," from phrase per fidem decipere "to deceive through trustingness," from per "through" (from PIE root *per- (1) "forward," hence "through") + fidem (nominative fides) "faith" (from PIE root *bheidh- "to trust, confide, persuade").

[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"]
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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" (from PIE root *bheidh- "to trust, confide, persuade"). 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.
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bide (v.)
Old English bidan "to stay, continue, live, remain," also "to trust, rely," from Proto-Germanic *bidan "to await" (source also of Old Norse biða, Old Saxon bidan, Old Frisian bidia, Middle Dutch biden, Old High German bitan, Gothic beidan "to wait"), which is of uncertain origin. Possibly from PIE root *bheidh- "to trust, confide, persuade" (via notion of "to await trustingly"). Preserved in Scotland and northern England, replaced elsewhere by abide in all senses except in expression bide (one's) time (c. 1840). Related: Bided; biding.
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confederation (n.)

early 15c., "act of confederating, alliance, agreement," from Anglo-French confederacion, Old French confederacion (14c.), from Late Latin confoederationem (nominative confoederatio), noun of action from past-participle stem of confoederare "to unite in a league," from assimilated form of com "with, together" (see con-) + foederare (from suffixed form of PIE root *bheidh- "to trust, confide, persuade").

Meaning "states or persons united by a league" is from 1620s. In U.S. history, the Articles of Confederation were adopted by Congress in 1777 and ratified by the states over the next four years. They went into effect March 1, 1781, and expired March 4, 1789.

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defy (v.)

c. 1300, defien, "to renounce one's allegiance;" mid-14c., "to challenge to fight, dare to meet in combat;" from Old French defier, desfier "to challenge, defy, provoke; renounce (a belief), repudiate (a vow, etc.)," from Vulgar Latin *disfidare "renounce one's faith" (in Medieval Latin diffidare), from Latin dis- "away" (see dis-) + fidus "faithful" (from PIE root *bheidh- "to trust, confide, persuade"). By 1670s as "dare (someone) to do something (that the challenger believes cannot or will not be done)."

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diffidence (n.)
Origin and meaning of diffidence

c. 1400, "distrust, want of confidence, doubt of the ability or disposition of others," from Latin diffidentia "mistrust, distrust, want of confidence," from diffidere "to mistrust, lack confidence," from dis- "away" (see dis-) + fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). The opposite of confidence. Original sense (distrust of others) is obsolete; the modern sense is of "distrust of oneself, want of confidence in one's ability, worth, or fitness" (1650s), hence "retiring disposition, modest reserve."  

Diffidence is a defect: it is an undue distrust of self, with fear of being censured for failure, tending to unfit one for duty. [Century Dictionary]
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self-confident (adj.)
1610s, from self- + confident. Related: self-confidently.
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confidential (adj.)

1759, "indicating the confiding of a private intimacy," from Latin confidentia (see confidence) + -al (1). Sense of "intended to be treated as private" is from 1773; that of "enjoying the confidence of another" is from 1805. Related: Confidentially.

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confidentiality (n.)

"quality of being confidential," 1830; see confidential + -ity.

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