1. A modified muscular pouch behind the stomach in the digestive tract of birds, having a thick lining and often containing ingested grit that aids in the breakdown of seeds and other hard materials by grinding them down before digestion.
2. A similar digestive organ found in certain invertebrates, such as the earthworm.
[Alteration of Middle English giser, from Old French, from Vulgar Latin *gicērium, from Latin gigēria, cooked entrails of poultry, probably of Iranian origin; akin to Persian jigar, liver; see ykw in the Appendix of Indo-European roots.]
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