"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"]
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.
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)."
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 Original sense (distrust of others) is obsolete; the modern sense is of "distrust of oneself, want of confidence in one's ability, worth, or fitness" (1650s), hence "retiring disposition, modest reserve."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]