Source : Webster's Revised Unabridged Dictionary (1913)

Moonfish \Moon"fish`\, n. (Zo["o]l.)
   (a) An American marine fish ({Vomer setipennis}); -- called
       also {bluntnosed shiner}, {horsefish}, and {sunfish}.
   (b) A broad, thin, silvery marine fish ({Selene vomer}); --
       called also {lookdown}, and {silver moonfish}.
   (c) The mola. See {Sunfish}, 1.

Source : WordNet®

moonfish
     n 1: any of several silvery marine fishes with very flat bodies
          [syn: {Atlantic moonfish}, {horsefish}, {horsehead}, {horse-head},
           {dollarfish}, {Selene setapinnis}]
     2: large elliptical brightly colored deep-sea fish of Atlantic
        and Pacific and Mediterranean [syn: {opah}, {Lampris
        regius}]
     [also: {moonfishes} (pl)]