1. A segmental, modified appendage which serves as a jaw in arthropods or an invertebrate animal that has jointed limbs, a segmented body, and an exoskeleton made of chitin; such as, an insect, arachnid, centipede, or crustacean.
2. Any leglike appendage of a crustacean, when modified wholly, or in part, to serve as a jaw; especially, one of the maxillipeds or one of the six specialized feeding appendages arranged in pairs and located just behind the maxillae (upper jawbone) on the heads of crustaceans.