The Collaborative International Dictionary of English v.0.48:

Discern \Dis*cern"\, v. t. [imp. & p. p. Discerned; p. pr. &
   vb. n. Discerning.] [F. discerner, L. discernere,
   discretum; dis- + cernere to separate, distinguish. See
   Certain, and cf. Discreet.]
   1. To see and identify by noting a difference or differences;
      to note the distinctive character of; to discriminate; to
      distinguish.
      [1913 Webster]

            To discern such buds as are fit to produce blossoms.
                                                  --Boyle.
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            A counterfeit stone which thine eye can not discern
            from a right stone.                   --Robynson
                                                  (More's
                                                  Utopia).
      [1913 Webster]

   2. To see by the eye or by the understanding; to perceive and
      recognize; as, to discern a difference.
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            And [I] beheld among the simple ones, I discerned
            among the youths, a young man void of understanding.
                                                  --Prov. vii.
                                                  7.
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            Our unassisted sight . . . is not acute enough to
            discern the minute texture of visible objects.
                                                  --Beattie.
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            I wake, and I discern the truth.      --Tennyson.

   Syn: To perceive; distinguish; discover; penetrate;
        discriminate; espy; descry; detect. See Perceive.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Discern \Dis*cern"\, v. i.
   1. To see or understand the difference; to make distinction;
      as, to discern between good and evil, truth and falsehood.
      [1913 Webster]

            More than sixscore thousand that cannot discern
            between their right hand their left.  --Jonah iv.
                                                  11.
      [1913 Webster]

   2. To make cognizance. [Obs.] --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

discern
    v 1: detect with the senses; "The fleeing convicts were picked
         out of the darkness by the watchful prison guards"; "I
         can't make out the faces in this photograph" [syn: spot,
         recognize, recognise, distinguish, discern, pick
         out, make out, tell apart]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "discern":
   anticipate, appreciate, apprehend, ascertain, be acquainted with,
   be apprised of, be aware of, be cognizant of, be conscious of,
   be conversant with, be informed, behold, catch sight of,
   clap eyes on, cognize, come alive, comprehend, conceive,
   conceptualize, descry, detect, difference, differentiate, discover,
   discriminate, distinguish, divine, espy, extricate, fathom,
   foresee, glimpse, grasp, have, have in sight,
   have information about, have knowledge of, identify, ken, know,
   lay eyes on, look on, look upon, make out, note, notice, observe,
   penetrate, perceive, pick out, pick up, pierce, plumb, possess,
   prehend, realize, recognize, remark, savvy, see, see daylight,
   see into, see the light, see through, seize, sense, separate,
   sever, sight, spot, spy, take in, twig, understand, view, witness,
   wot, wot of