The Collaborative International Dictionary of English v.0.48:

Perspicacious \Per`spi*ca"cious\ (p[~e]r`sp[i^]*k[=a]"sh[u^]s),
   a. [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.
      [1913 Webster]

   2. Fig.: Of acute discernment; keen.
      [1913 Webster] -- Per`spi*ca"cious*ly, adv. --
      Per`spi*ca"cious*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

perspicacious
    adj 1: acutely insightful and wise; "much too perspicacious to
           be taken in by such a spurious argument"; "observant and
           thoughtful, he was given to asking sagacious questions";
           "a source of valuable insights and sapient advice to
           educators" [syn: perspicacious, sagacious, sapient]
    2: mentally acute or penetratingly discerning; "too clear-eyed
       not to see what problems would follow"; "chaos could be
       prevented only by clear-sighted leadership"; "much too
       perspicacious to be taken in by so spurious an argument"
       [syn: clear-eyed, clear-sighted, perspicacious]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "perspicacious":
   acute, all-knowing, apperceptive, appercipient, apprehending,
   apprehensive, argute, astute, aware, cagey, cogent, cognizant,
   comprehending, conscious, discerning, farseeing, farsighted,
   foreseeing, foresighted, forethoughted, forethoughtful, heady,
   incisive, insightful, intelligent, judicious, knowing,
   knowledgeable, longheaded, longsighted, mindful, omniscient,
   penetrating, perceptive, percipient, perspicuous, piercing,
   prehensile, provident, sagacious, savvy, sensible, sharp-sighted,
   sharp-witted, shrewd, trenchant, understanding, wise