acuity
n.
early 15c., from Middle French acuité (16c.) or directly from Medieval Latin acuitatem (nominative acuitas) "sharpness," from Latin acuere "to sharpen," related to acus "needle," acuere "to sharpen," from PIE root *ak- "rise to a point, be sharp" (see acrid).
〔李〕[acu =sharp尖的；-ity →] n.the condition or quality of being sharp；sharpness of mind or senses尖锐；敏锐；锐利
〔李〕[acu;-ityn.] n.尖锐； 敏锐 ←acu (L acus)=needle 针