formerly also endoctrinate, 1620s, "to teach," formed as if from Latin (but there seems to have been no word *indoctrinare), perhaps modeled on French endoctriner or extended from earlier (now obsolete) verb indoctrine, endoctrine, "to instruct" (mid-15c.); see in- (2) "in" + doctrine + -ate (2)). Meaning "to imbue with an idea or opinion" first recorded 1832. Related: Indoctrinated; indoctrinating.

1640s, "instruction," noun of action from indoctrinate. In reference to imbuing with opinions or ideology, from 1865.

also indue, c. 1400, "invest (with) some gift, quality, or power" (usually passive), from Old French enduire, induire "lead, drive, initiate, indoctrinate" (12c.) and directly from Latin inducere "to lead" (see induce). Related: Endued.