mandible vs lower jaw

mandible and lower jaw both are nouns.

Word	Noun	Adjective	Verb	Adverb
mandible	Yes	No	No	No
lower jaw	Yes	No	No	No

As nouns, mandible and lower jaw are synonyms defined as:

mandible and lower jaw: the jaw in vertebrates that is hinged to open the mouth

Other synonyms of mandible include jawbone, jowl, lower jawbone, mandibula, mandibular bone, submaxilla.

mandible (noun)	lower jaw (noun)
the jaw in vertebrates that is hinged to open the mouth	the jaw in vertebrates that is hinged to open the mouth