His remarkable memory has lost its acuity, and he tires easily.
The unblinking electronic eye was an extension of his own reflexes and acuity—when the red light went on, all else was excluded.
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).
acuity a·cu·i·ty (ə-kyōō'ĭ-tē)
Sharpness, clearness, and distinctness of perception or vision.