axillary fossa vs axilla

axillary fossa and axilla both are nouns.

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

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

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

Other synonyms of axillary fossa include armpit, axillary cavity.

axillary fossa (noun)	axilla (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