Is it ensure, insure, or assure?
Old English nearu "narrow, constricted, limited; petty; causing difficulty, oppressive; strict, severe," from West Germanic *narwaz "narrowness" (cf. Frisian nar, Old Saxon naru, Middle Dutch nare, Dutch naar); not found in other Germanic languages and of unknown origin. The narrow seas (c.1400) were the waters between Great Britain and the continent and Ireland. Related: Narrowness.
Old English nearwian "to force in, cramp, confine; become smaller, shrink;" see narrow (adj.). Related: Narrowed; narrowing.
c.1200, nearewe "narrow part, place, or thing," from narrow (adj.). Old English nearu (n.) meant "danger, distress, difficulty," also "prison, hiding place."