Is it ensure, insure, or assure?
c.1300, from Old French aprentiz "someone learning" (13c., Modern French apprenti, taking the older form as a plural), also as an adjective, "unskilled, inexperienced," from aprendre (Modern French apprendre) "to learn; to teach," contracted from Latin apprehendere (see apprehend). Shortened form prentice long was more usual in English.
1630s, from apprentice (n.). Related: Apprenticed; apprenticing.