The Collaborative International Dictionary of English v.0.48:

Silversides \Sil"ver*sides`\, n. (Zool.)
   Any one of several species of small fishes of the family
   Atherinidae, having a silvery stripe along each side of the
   body. The common species of the American coast (Menidia
   notata) is very abundant. Called also silverside, sand
   smelt, friar, tailor, and tinker.
   [1913 Webster]

   Brook silversides (Zool.), a small fresh-water North
      American fish (Labadesthes sicculus) related to the
      marine silversides.
      [1913 Webster]

WordNet (r) 3.0 (2006):

silverside
    n 1: small fishes having a silver stripe along each side;
         abundant along the Atlantic coast of the United States
         [syn: silversides, silverside]