1550s, "a disowning," from Latin abdicationem (nominative abdicatio) "voluntary renunciation, abdication," noun of action from past-participle stem of abdicare "disown, disavow, reject," from ab "off, away from" (see ab-) + dicare "proclaim" (from PIE root *deik- "to show," also "pronounce solemnly," and see diction). Sense of "resignation of inherent sovereignty" is from 1680s.