1530s, a back-formation from imitation or imitator, or else from Latin imitatus, past participle of imitari "to copy, portray" (from PIE root *aim- "to copy"). Related: Imitated; imitating. An Old English word for this was æfterhyrigan.
c. 1400, "emulation; act of copying," from Old French imitacion, from Latin imitationem (nominative imitatio) "a copying, imitation," noun of action from past participle stem of imitari "to copy, portray, imitate," from PIE *im-eto-, from root *aim- "to copy." Meaning "an artificial likeness" is from c. 1600. As an adjective, from 1840.