Is it ensure, insure, or assure?
c.1300, maimen, from Old French mahaignier "injure, wound, muitilate, cripple, disarm," possibly from Vulgar Latin *mahanare (cf. Provençal mayanhar, Italian magagnare), of unknown origin; or possibly from a Germanic source, from Proto-Germanic *mait- (cf. Old Norse meiða "to hurt," related to mad (adj.)), or from PIE root *mai- "to cut." Related: Maimed; maiming.