The Collaborative International Dictionary of English v.0.48:

Acuity \A*cu"i*ty\, n. [LL. acuitas: cf. F. acuit['e].]
   Sharpness or acuteness, as of a needle, wit, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acuity
    n 1: sharpness of vision; the visual ability to resolve fine
         detail (usually measured by a Snellen chart) [syn:
         acuity, visual acuity, sharp-sightedness]
    2: a quick and penetrating intelligence; "he argued with great
       acuteness"; "I admired the keenness of his mind" [syn:
       acuteness, acuity, sharpness, keenness]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "acuity":
   acridity, acumen, acumination, acuteness, adroitness, agility,
   alertness, apperception, aptitude, aptness, astuteness, attention,
   attentiveness, braininess, brightness, brilliance, clear thinking,
   cleverness, cogency, dexterity, discernment, edge, esprit,
   farseeingness, farsightedness, flair, foresight, foresightedness,
   genius, giftedness, gifts, incisiveness, insight, keen-wittedness,
   keenness, longheadedness, longsightedness, mental alertness,
   mercurial mind, mucronation, native cleverness, nimble mind,
   nimble-wittedness, nimbleness, nous, penetration, perception,
   perceptiveness, percipience, perspicaciousness, perspicacity,
   perspicuity, perspicuousness, pointedness, prickliness,
   promptitude, promptness, providence, punctuality, quick parts,
   quick thinking, quick wit, quick-wittedness, quickness, readiness,
   ready wit, sagaciousness, sagacity, savvy, sensibility,
   sharp-wittedness, sharpness, sleeplessness, smartness, smarts,
   spinosity, sprightly wit, talent, thorniness, trenchancy,
   wakefulness