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."
late 12c., "a feudal superior, ruler possessing the fealty of other rulers," from over- + lord (n.). In English history, especially a king of one of the Anglo-Saxon realms who held pre-eminence or authority over some of the other kings and chiefs. The word was chosen in 1943 as the Allied code-word for the invasion of western Europe that resulted in D-Day.
In the perspective of 'Overlord,' that one huge hazardous offensive operation on which, it seemed, the fate of the world depended, smaller adventures receded to infinitesimal importance. [Evelyn Waugh, "Unconditional Surrender"]
c. 1200, devocioun, "profound religious emotion, awe, reverence," from Old French devocion "devotion, piety" and directly from Latin devotionem (nominative devotio), noun of action from past-participle stem of devovere "dedicate by a vow, sacrifice oneself, promise solemnly," from de "down, away" (see de-) + vovere "to vow" (see vow (n.)). From late 14c. as "an act of religious worship, a religious exercise" (now usually devotions).
In ancient Latin, "act of consecrating by a vow," also "loyalty, fealty, allegiance;" in Church Latin, "devotion to God, piety." The application to secular situations came to English via Italian and French; sense of "act of setting apart or consecrating" is from c. 1500.