The Collaborative International Dictionary of English v.0.48:

Percipient \Per*cip"i*ent\, a. [L. percipiens, -entis, p. pr. of
   percipere. See Perceive.]
   Having the faculty of perception; perceiving; as, a
   percipient being. --Bentley. -- n. One who, or that which, is
   percipient. --Glanvill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

percipient
    adj 1: characterized by ease and quickness in perceiving; "clear
           mind"; "a percipient author" [syn: clear, percipient]
    n 1: a person who becomes aware (of things or events) through
         the senses [syn: perceiver, percipient, observer,
         beholder]

Moby Thesaurus II by Grady Ward, 1.0:

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