Is it ensure, insure, or assure?
1707, "a quick thrust after parrying a lunge," a fencing term, from French riposte, by dissimilation from risposte (17c.), from Italian risposta "a reply," noun use of fem. past participle of rispondere "to respond," from Latin respondere (see respond). Sense of "sharp retort; quick, sharp reply," is first attested 1865. As a verb, 1851.