armpit vs axillary cavity

armpit and axillary cavity both are nouns.

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

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

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

Other synonyms of armpit include axilla, axillary fossa.

armpit (noun)	axillary cavity (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