Is it ensure, insure, or assure?
1530s, a back-formation from protraction and in part from Latin protractus, past participle of protrahere "to draw forth, prolong." Etymologically identical with portray, which was altered in French. Related: Protracted; protracting.
protract pro·tract (prō-trākt', prə-)v. pro·tract·ed, pro·tract·ing, pro·tracts To extend or protrude a body part.