The Collaborative International Dictionary of English v.0.48:

Smelt \Smelt\, n. [AS. smelt, smylt; akin to Dan. smelt.]
   1. (Zool.) Any one of numerous species of small silvery
      salmonoid fishes of the genus Osmerus and allied genera,
      which ascend rivers to spawn, and sometimes become
      landlocked in lakes. They are esteemed as food, and have a
      peculiar odor and taste.
      [1913 Webster]

   Note: The most important species are the European smelt
         (Osmerus eperlans) (called also eperlan,
         sparling, and spirling), the Eastern American smelt
         (Osmerus mordax), the California smelt (Osmerus
         thalichthys), and the surf smelt (Hypomesus olidus).
         The name is loosely applied to various other small
         fishes, as the lant, the California tomcod, the spawn
         eater, the silversides.
         [1913 Webster]

   2. Fig.: A gull; a simpleton. [Obs.] --Beau. & Fl.
      [1913 Webster]

   Sand smelt (Zool.), the silverside.
      [1913 Webster]