1540s, "act of shouting or applauding in approval," from Latin acclamationem (nominative acclamatio) "a calling, exclamation, shout of approval," noun of action from past-participle stem of acclamare "to call to, cry out at, shout approval or disapproval of," from assimilated form of ad "to, toward" (see ad-) + clamare "cry out" (from PIE root *kele- (2) "to shout"). As a method of spontaneous approval of resolutions, etc., by unanimous voice vote, by 1801, probably from the French Revolution.