frailness vs infirmity

frailness and infirmity both are nouns.

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

As nouns, frailness and infirmity are synonyms defined as:

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

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

frailness (noun)	infirmity (noun)
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)