Is it ensure, insure, or assure?
late 14c., "parti-colored" (originally of fabric), from Anglo-French motteley, probably from Old English mot "speck" (see mote). But Klein's sources say probably from Gaulish. "Diversified in color," especially of a fool's dress. Hence, allusively, "a fool" (1600). As a noun meaning "cloth of mixed color" from late 14c.