maxilla vs upper jaw

maxilla and upper jaw both are nouns.

Word	Noun	Adjective	Verb	Adverb
maxilla	Yes	No	No	No
upper jaw	Yes	No	No	No

As nouns, maxilla and upper jaw are synonyms defined as:

maxilla and upper jaw: the jaw in vertebrates that is fused to the cranium

Other synonyms of maxilla include maxillary, upper jawbone.

maxilla (noun)	upper jaw (noun)
the jaw in vertebrates that is fused to the cranium	the jaw in vertebrates that is fused to the cranium