The Collaborative International Dictionary of English v.0.48:

Brit \Brit\, Britt \Britt\, n. (Zool.)
      (a) The young of the common herring; also, a small species
          of herring; the sprat.
      (b) The minute marine animals (chiefly Entomostraca) upon
          which the right whales feed.
          [1913 Webster]

WordNet (r) 3.0 (2006):

Brit
    n 1: a native or inhabitant of Great Britain [syn: Britisher,
         Briton, Brit]
    2: the young of a herring or sprat or similar fish [syn: brit,
       britt]
    3: minute crustaceans forming food for right whales [syn:
       brit, britt]