(1):
(n.) A thick muscular stomach found in many invertebrate animals.
(2):
(n.) 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.
(3):
(n.) A stomach armed with chitinous or shelly plates or teeth, as in certain insects and mollusks.