Is it ensure, insure, or assure?
"concerning, about," early 13c., onont "on level with," also "in the company of, fronting against," from Old English on efn "near to, close by," originally "on even (ground) with;" the parasitic -t added 12c. A northern form (in Midlands, anenst, with adverbial genitive), affected by English writers in Scottish sense of "in respect or reference to." Cf. German neben "near to, by the side of," short for in eben, from Old High German ebani "equality."