Is it ensure, insure, or assure?
late 15c., "instrument for bending," agent noun from bend (v.). Slang meaning "drinking bout" is American English, attested from 1846, perhaps from the Scottish sense of "a hard drinker" (1728).
ear-bender, elbow-bender, fender-bender, mind-blower, pretzel-bender
[Underworld 1940s+; first sense fr hell-bender, ''alligator,'' of obscure origin, which came to mean ''anything spectacular and superior'' and was applied to a great spree in the mid-19th century]