Is it ensure, insure, or assure?
late 13c., probably from Old Norse hvirfla "to go round, spin," related to hvirfill "circle, ring, crown," and to Old English hweorfan "to turn" (see whir). Related: Whirled; whirling. Whirlybird "helicopter" is from 1951.
early 15c., "flywheel of a spindle," from whirl (v.). The meaning "act of whirling" is recorded from late 15c.; figurative sense of "confused activity" is recorded from 1550s. Colloquial sense of "tentative attempt" is attested from 1884, American English.