1. The lower jaw of a vertebrate animal.
2. Either the upper or lower part of the beak in birds.
3. Any of various mouth organs of invertebrates used for seizing and biting food, especially either of a pair of such organs in insects and other arthropods.

[Middle English, from Old French, from Late Latin mandibula, from Latin mandere, to chew.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.