mandibular fossa vs fossa

mandibular fossa and fossa both are nouns.

Word	Noun	Adjective	Verb	Adverb
mandibular fossa	Yes	No	No	No
fossa	Yes	No	No	No

As nouns, fossa is a hypernym of mandibular fossa; that is, fossa is a word with a broader meaning than mandibular fossa:

mandibular fossa: a deep concavity in the temporal bone at the root of the zygomatic arch that receives the condyle of the mandible
fossa: a concavity in a surface (especially an anatomical depression)

Other hypernyms of mandibular fossa include pit.

mandibular fossa (noun)	fossa (noun)
a deep concavity in the temporal bone at the root of the zygomatic arch that receives the condyle of the mandible	largest carnivore of Madagascar; intermediate in some respects between cats and civets
	a concavity in a surface (especially an anatomical depression)