Perspicacious, a.
Etymology: [L. perspicax, -acis, fr. perspicere to look through: cf. F. perspicace. See Perspective.]
1. Having the power of seeing clearly; quick-sighted; sharp of sight.
2. Fig.: Of acute discernment; keen. -- Per`spi*ca"cious*ly, adv. -- Per`spi*ca"cious*ness, n.
Shades of meaning
Fernald has no entry of its own for perspicacious; he lists it under astute, sagacious.
He lists it without comment; the entries above explain its neighbors.