Is it ensure, insure, or assure?
early 14c., "pass across, over, or through," from Old French traverser "to cross, thwart" (11c.), from Vulgar Latin *traversare, from Latin transversare "to cross, throw across," from Latin transversus "turn across" (see transverse). The noun meaning "act of passing through a gate, crossing a bridge, etc." is recorded from mid-14c.; meaning "a passage by which one may traverse" is recorded from 1670s. Military foritifcation sense of "barrier, barricade" is recorded from 1590s. Related: Traversed; traversing.