What is "gizzard shad"

Gizzard \Giz"zard\, n. [F. g['e]sier, L. gigeria, pl., the cooked entrails of poultry. Cf. Gigerium.]

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.

2. (Zo["o]l.)

   1. A thick muscular stomach found in many invertebrate animals.

   2. A stomach armed with chitinous or shelly plates or teeth, as in certain insects and mollusks.

      Gizzard shad (Zo["o]l.), 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]