Is it ensure, insure, or assure?
1570s, "discharge of a number of guns at once," from Middle French volee "flight" (12c.), from Vulgar Latin *volta, fem. noun from Latin volatum, past participle of volare "to fly" (see volant). Sporting sense (originally in tennis) is from 1819 (v.), 1862 (n.), from notion of hitting the ball in flight.
volley vol·ley (vŏl'ē)
The bursting forth of many things together, such as a synchronous group of impulses induced simultaneously by artificial stimulation of either nerve fibers or muscle fibers.