Is it ensure, insure, or assure?
to cause to accept a belief or idea through repetition
Latin in- + calcare 'to trample'
1540s, from Latin inculcatus, past participle of inculcare "force upon, stamp in, tread down," from in- "in" (see in- (2)) + calcare "to tread, press in," from calx (1) "heel." Related: Inculcated; inculcating.