infirmity vs asthenia

infirmity and asthenia both are nouns.

Word	Noun	Adjective	Verb	Adverb
infirmity	Yes	No	No	No
asthenia	Yes	No	No	No

As nouns, asthenia is a hyponym of infirmity; that is, asthenia is a word with a more specific, narrower meaning than infirmity:

infirmity: the state of being weak in health or body (especially from old age)
asthenia: an abnormal loss of strength

Other hyponyms of infirmity include astheny, cachexia, cachexy, wasting, sickliness.

infirmity (noun)	asthenia (noun)
the state of being weak in health or body (especially from old age)	an abnormal loss of strength