Is it ensure, insure, or assure?
masc. proper name, from French Nicolas, from Latin Nicholaus, Nicolaus, from Greek Nikholaos, literally "victory-people," from nike "victory" (see Nike) + laos "people" (see lay (adj.)). The saint (obit. 326 C.E.) was a bishop of Myra in Lycia, patron of scholars, especially schoolboys. A popular given name in England in Middle Ages, as was the fem. form Nicolaa, corresponding to French Nicole. Colloquial Old Nick "the devil" is attested from 1640s, evidently from the proper name, but for no certain reason.