Is it ensure, insure, or assure?
"attendant suitor of a lady," 1720, from French beau "the beautiful," noun use of an adjective, from Old French bel "beautiful, handsome, fair, genuine, real" (11c.), from Latin bellus "handsome, fine, pretty, agreeable," diminutive of bonus "good" (see bene-). Meaning "man who attends excessively to dress, etiquette, etc.; a fop; a dandy" is from 1680s, short for French beau garçon "pretty boy" (1660s).