acuity (n.) Look up acuity at Dictionary.com
"sharpness, acuteness," early 15c., from Old French acuite (14c.) or directly from Medieval Latin acuitatem (nominative acuitas) "sharpness," noun of state from Latin acuere "to sharpen," literal and figurative (of intellect, emotion, etc.), related to acus "a needle," from PIE root *ak- "rise to a point, be sharp" (see acro-).