axilla vs axillary fossa

axilla and axillary fossa both are nouns.

Word	Noun	Adjective	Verb	Adverb
axilla	Yes	No	No	No
axillary fossa	Yes	No	No	No

As nouns, axilla and axillary fossa are synonyms defined as:

axilla and axillary fossa: the hollow under the arm where it is joined to the shoulder

Other synonyms of axilla include armpit, axillary cavity.

axilla (noun)	axillary fossa (noun)
the hollow under the arm where it is joined to the shoulder	the hollow under the arm where it is joined to the shoulder