The Collaborative International Dictionary of English v.0.48:

Perception \Per*cep"tion\ (p[~e]r*s[e^]p"sh[u^]n), n. [L.
   perceptio: cf. F. perception. See Perceive.]
   1. The act of perceiving; cognizance by the senses or
      intellect; apprehension by the bodily organs, or by the
      mind, of what is presented to them; discernment;
      apprehension; cognition.
      [1913 Webster]

   2. (Metaph.) The faculty of perceiving; the faculty, or
      peculiar part, of man's constitution by which he has
      knowledge through the medium or instrumentality of the
      bodily organs; the act of apperhending material objects or
      qualities through the senses; -- distinguished from
      conception. --Sir W. Hamilton.
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            Matter hath no life nor perception, and is not
            conscious of its own existence.       --Bentley.
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   3. The quality, state, or capability, of being affected by
      something external; sensation; sensibility. [Obs.]
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            This experiment discovereth perception in plants.
                                                  --Bacon.
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   4. An idea; a notion. [Obs.] --Sir M. Hale.
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   Note: "The word perception is, in the language of
         philosophers previous to Reid, used in a very extensive
         signification. By Descartes, Malebranche, Locke,
         Leibnitz, and others, it is employed in a sense almost
         as unexclusive as consciousness, in its widest
         signification. By Reid this word was limited to our
         faculty acquisitive of knowledge, and to that branch of
         this faculty whereby, through the senses, we obtain a
         knowledge of the external world. But his limitation did
         not stop here. In the act of external perception he
         distinguished two elements, to which he gave the names
         of perception and sensation. He ought perhaps to have
         called these perception proper and sensation proper,
         when employed in his special meaning." --Sir W.
         Hamilton.
         [1913 Webster]

WordNet (r) 3.0 (2006):

perception
    n 1: the representation of what is perceived; basic component in
         the formation of a concept [syn: percept, perception,
         perceptual experience]
    2: a way of conceiving something; "Luther had a new perception
       of the Bible"
    3: the process of perceiving
    4: knowledge gained by perceiving; "a man admired for the depth
       of his perception"
    5: becoming aware of something via the senses [syn: sensing,
       perception]

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "perception":
   acuity, acumen, acuteness, apperception, appreciation,
   appreciativeness, apprehension, astuteness, awareness, clear sight,
   cogency, cognition, cognizance, color vision, comprehension,
   conceit, concept, conception, cone vision, consciousness,
   critical discernment, day vision, daylight vision, discernment,
   experience, eye, eye-mindedness, eyesight, fancy, farseeingness,
   farsight, farsightedness, feel, feeling, field of view,
   field of vision, flair, foresight, foresightedness, grasp, horizon,
   idea, image, imago, impression, incisiveness, insight, instinct,
   intellection, intellectual object, intuition, judgment, keen sight,
   ken, knowledge, longheadedness, longsightedness, memory-trace,
   mental image, mental impression, mindfulness, night vision, noesis,
   note, notice, notion, observation, opinion, penetration, percept,
   perceptiveness, percipience, peripheral field, peripheral vision,
   perspective, perspicaciousness, perspicacity, perspicuity,
   perspicuousness, photopia, power of sight, providence, purview,
   quick sight, range, realization, recept, recognition, reflection,
   representation, response, response to stimuli, rod vision,
   sagaciousness, sagacity, scope, scotopia, seeing, sensation, sense,
   sense impression, sense of sight, sense perception, sensibility,
   sensory experience, sentiment, sight, sightedness, supposition,
   sweep, theory, thought, trenchancy, twilight vision, understanding,
   unobstructed vision, view, vision, visual acuity, visual field,
   visual sense