The Collaborative International Dictionary of English v.0.48:

lookdown \look"down`\, look-down \look"-down`\, n. (Zool.)
   A fish (Selene vomer) similar to the moonfish but with eyes
   high on the truncated forehead; it was also called moonfish
   at one time.

   Syn: Selene vomer.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Moonfish \Moon"fish`\, n. (Zool.)
   (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.
       [1913 Webster]