perspicacity (n.)

"state or character of being perspicacious; keenness of sight, clearness of understanding," 1540s, from French perspicacité (15c.) and directly from Late Latin perspicacitas "sharp-sightedness, discernment," from Latin perspicax "sharp-sighted, having the power of seeing through," from perspicere "look through, look closely at," from per "through" (from PIE root *per- (1) "forward," hence "through") + specere "look at" (from PIE root *spek- "to observe"). An earlier word was perspicience "ability to see all things, infinite vision" (c. 1400).