Is it ensure, insure, or assure?
c.1300, "madness, insanity; fit of frenzy; anger, wrath; fierceness in battle; violence of storm, fire, etc.," from Old French rage, raige "spirit, passion, rage, fury, madness" (11c.), from Medieval Latin rabia, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave" (cf. rabies, which originally had this sense), from PIE *rebh- "violent, impetuous" (cf. Old English rabbian "to rage"). Similarly, Welsh (cynddaredd) and Breton (kounnar) words for "rage, fury" originally meant "hydrophobia" and are compounds based on the word for "dog" (Welsh ci, plural cwn; Breton ki). In 15c.-16c. it also could mean "rabies." The rage "fashion, vogue" dates from 1785.
mid-13c., "to play, romp," from rage (n.). Meanings "be furious; speak passionately; go mad" first recorded c.1300. Of things from 1530s. Related: Raged; raging.
A good party: This is a rage, man (Australian 1980+, Canadian 1990s+)