Source : Webster's Revised Unabridged Dictionary (1913)

Butterball \But"ter*ball`\, n. (Zo["o]l.)
   The buffel duck.

Source : WordNet®

butterball
     n 1: a rotund individual [syn: {fatso}, {fatty}, {fat person}, {roly-poly}]
          [ant: {thin person}]
     2: small North American diving duck; males have bushy head
        plumage [syn: {bufflehead}, {dipper}, {Bucephela albeola}]