The Collaborative International Dictionary of English v.0.48:

Gizzard \Giz"zard\, n. [F. g['e]sier, L. gigeria, pl., the
   cooked entrails of poultry. Cf. Gigerium.]
   [1913 Webster]
   1. (Anat.) The second, or true, muscular stomach of birds, in
      which the food is crushed and ground, after being softened
      in the glandular stomach (crop), or lower part of the
      esophagus; the gigerium.
      [1913 Webster]

   2. (Zool.)
      (a) A thick muscular stomach found in many invertebrate
          animals.
      (b) A stomach armed with chitinous or shelly plates or
          teeth, as in certain insects and mollusks.
          [1913 Webster]

   Gizzard shad (Zool.), an American herring (Dorosoma
      cepedianum) resembling the shad, but of little value.

   To fret the gizzard, to harass; to vex one's self; to
      worry. [Low] --Hudibras.

   To stick in one's gizzard, to be difficult of digestion; to
      be offensive. [Low]
      [1913 Webster]