acuity vs twenty-twenty

acuity and twenty-twenty both are nouns.

Word	Noun	Adjective	Verb	Adverb
acuity	Yes	No	No	No
twenty-twenty	Yes	No	No	No

As nouns, twenty-twenty is a hyponym of acuity; that is, twenty-twenty is a word with a more specific, narrower meaning than acuity:

acuity: sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart)
twenty-twenty: normal visual acuity, as measured by the ability to read charts at a distance of 20 feet

Other hyponyms of acuity include 20/20, oxyopia.

acuity (noun)	twenty-twenty (noun)
a quick and penetrating intelligence	normal visual acuity, as measured by the ability to read charts at a distance of 20 feet
sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart)