1. (Science: anatomy, ornithology) 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 oesophagus; the gigerium.
3. (Science: zoology) gizzard shad, 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. To stick in one's gizzard, to be difficult of digestion; to be offensive.