Is it ensure, insure, or assure?
1580s, from Middle French harlequin, from Old French Herlequin, Hellequin, etc., leader of la maisnie Hellequin, a troop of demons who rode the night air on horses. He corresponds to Old English Herla cyning "King Herla," mythical character sometimes identified as Woden; possibly also the same as the German Erlkönig "Elf King" of the Goethe poem. Sometimes also associated with Herrequin, 9c. count of Boulogne, who was proverbially wicked. In English pantomime, a mute character who carries a magic wand. His Italian form, arlecchino, is one of the stock characters of commedia del'arte. From his ludicrous dress comes the English adjective meaning "particolored" (1779).