perspicacious (adj.) Look up perspicacious at Dictionary.com
1630s, formed as an adjective to perspicacity, from Latin perspicax "sharp-sighted, having the power of seeing through; acute," 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"). Related: Perspicaciously; perspicaciousness.