mandible āļāļ·āļāļāļ°āđāļĢ mandible āļāļ·āļāļāļ°āđāļĢ The lower jaw of a vertebrate animal.Either the upper or lower part of the beak in birds.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.