Is it ensure, insure, or assure?
1680s, diminutive of Scottish dialectal bun, pet name for "rabbit," previously (1580s) for "squirrel," and also a term of endearment for a young attractive woman or child (c.1600). Ultimately it could be from Scottish bun "tail of a hare" (1530s), or from French bon, or from a Scandinavian source. The Playboy Club hostess sense is from 1960. The Bunny Hug (1912), along with the foxtrot and the Wilson glide, were among the popular/scandalous dances of the ragtime era.