axillary fossa vs armpit

axillary fossa and armpit both are nouns.

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

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

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

Other synonyms of axillary fossa include axilla, axillary cavity.

axillary fossa (noun)	armpit (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