lower jaw

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The part of the face below the mouth; the jaw.
• noun Specifically, the bone therein; the mandible of humans and other vertebrates that, with the cranium, composes the skull.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the jaw in vertebrates that is hinged to open the mouth