Is it ensure, insure, or assure?
late 14c., "to gallop," possibly from Old North French *waloper (13c.), probably from Frankish *walalaupan "to run well" (cf. Old High German wela "well" and Old Low Franconian loupon "to run, leap"). The meaning "to thrash" (1820) and the noun meaning "heavy blow" (1823) may be separate developments, of imitative origin. Related: Walloped; walloping.