feebleness vs infirmity

feebleness and infirmity both are nouns.

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

As nouns, feebleness and infirmity are synonyms defined as:

feebleness and infirmity: the state of being weak in health or body (especially from old age)

Other synonyms of feebleness include debility, frailness, frailty, valetudinarianism.

feebleness (noun)	infirmity (noun)
the quality of lacking intensity or substance	the state of being weak in health or body (especially from old age)
the state of being weak in health or body (especially from old age)