Is it ensure, insure, or assure?
mid-13c., "ornamental knob;" c.1300, "knob at the end of a sword hilt," from Old French pomel (12c., Modern French pommeau), "rounded knob," diminutive of pom "hilt of a sword," from Late Latin pomellum, diminutive of Latin pomum "apple" (see Pomona), the connecting notion being "roundness." Sense of "front peak of a saddle" first recorded mid-15c. In Middle English poetry it also sometimes meant a woman's breast. The gymnast's pommel horse is attested from 1908.