Is it ensure, insure, or assure?
1640s, "quick remark," from French repartie "an answering blow or thrust" (originally a fencing term), noun use of fem. past participle of Old French repartir "to reply promptly, start out again," from re- "back" (see re-) + partir "to part, depart, start" (see part (n.)). In 17c. often spelled reparty (see -ee). Meaning "a series of sharp rejoinders exchanged" is from 1680s.