Is it ensure, insure, or assure?
"one who has been initiated," 1811, from past participle adjective initiate (c.1600); see initiate (v.).
c.1600, "introduce to some practice or system," also "begin, set going," from Latin initiatus, past participle of initiare "to begin, originate," from initium "beginning" (see initial). In some senses a back-formation from initiation. Related: Initiated; initiates; initiating; initiator.