c. 1300, defamacioun, "disgrace, dishonor, ill repute" (senses now obsolete), from Old French diffamacion and directly from Medieval Latin deffamation, from Latin diffamationem (nominative diffamatio), noun of action from past-participle stem of diffamare "to spread abroad by ill report, make a scandal of," from dis-, here probably suggestive of ruination, + fama "a report, rumor" (from PIE root *bha- (2) "to speak, tell, say").
From late 14c. as "the wrong of injuring another's reputation without justification." From early 15c. as "calumny, slander, an instance of defaming."