perspicacity

noun3

1. •
   Acute discernment or understanding; insight.

   • "I understand," I said. "The fact is that you have the money." His face brightened. He seemed pleased at my perspicacity. — 1904
2. •
   The human faculty or power to mentally grasp or understand clearly.

   • His very veneration for his father-in-law, combined as it is with a total want of the most ordinary perspicacity, is an additional disqualification. — 1856
3. •
   (no longer used) Keen eyesight.