Is it ensure, insure, or assure?
"attacking" (1540s), "insulting" (1570s), both from Middle French offensif (16c.) and directly from Medieval Latin offensivus, from Latin offens-, past participle stem of offendere "offend" (see offend). Related: Offensively; offensiveness.
"condition of attacking, aggressive action," 1720, from offensive (adj.).