Source : Webster's Revised Unabridged Dictionary (1913)

Butterfish \But"ter*fish`\, n. (Zo["o]l.)
   A name given to several different fishes, in allusion to
   their slippery coating of mucus, as the {Stromateus
   triacanthus} of the Atlantic coast, the {Epinephelus
   punctatus} of the southern coast, the rock eel, and the
   kelpfish of New Zealand.

Source : WordNet®

butterfish
     n 1: any of numerous small flat Atlantic food fish having smooth
          skin
     2: small marine fish with a short smooth-scaled compressed body
        and feeble spines [syn: {stromateid fish}, {stromateid}]
     3: slippery scaleless food fish of the northern Atlantic
        coastal waters [syn: {rock gunnel}, {Pholis gunnellus}]
     [also: {butterfishes} (pl)]