infirmity vs cachexia

infirmity and cachexia both are nouns.

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

As nouns, cachexia is a hyponym of infirmity; that is, cachexia 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)
cachexia: any general reduction in vitality and strength of body and mind resulting from a debilitating chronic disease

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

infirmity (noun)	cachexia (noun)
the state of being weak in health or body (especially from old age)	any general reduction in vitality and strength of body and mind resulting from a debilitating chronic disease