The Collaborative International Dictionary of English v.0.48:

Distinguish \Dis*tin"guish\, v. t. [imp. & p. p.
   Distinguished; p. pr. & vb. n. Distinguishing.] [F.
   distinguer, L. distinguere, distinctum; di- = dis- +
   stinguere to quench, extinguish; prob. orig., to prick, and
   so akin to G. stechen, E. stick, and perh. sting. Cf.
   Extinguish.]
   1. Not set apart from others by visible marks; to make
      distinctive or discernible by exhibiting differences; to
      mark off by some characteristic.
      [1913 Webster]

            Not more distinguished by her purple vest,
            Than by the charming features of her face. --Dryden.
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            Milton has distinguished the sweetbrier and the
            eglantine.                            --Nares.
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   2. To separate by definition of terms or logical division of
      a subject with regard to difference; as, to distinguish
      sounds into high and low.
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            Moses distinguished the causes of the flood into
            those that belong to the heavens, and those that
            belong to the earth.                  --T. Burnet.
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   3. To recognize or discern by marks, signs, or characteristic
      quality or qualities; to know and discriminate (anything)
      from other things with which it might be confounded; as,
      to distinguish the sound of a drum.
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            We are enabled to distinguish good from evil, as
            well as truth from falsehood.         --Watts.
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            Nor more can you distinguish of a man,
            Than of his outward show.             --Shak.
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   4. To constitute a difference; to make to differ.
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            Who distinguisheth thee?              --1 Cor. iv.
                                                  7. (Douay
                                                  version).
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   5. To separate from others by a mark of honor; to make
      eminent or known; to confer distinction upon; -- with by
      or for."To distinguish themselves by means never tried
      before." --Johnson.

   Syn: To mark; discriminate; differentiate; characterize;
        discern; perceive; signalize; honor; glorify.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Distinguish \Dis*tin"guish\, v. i.
   1. To make distinctions; to perceive the difference; to
      exercise discrimination; -- with between; as, a judge
      distinguishes between cases apparently similar, but
      differing in principle.
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   2. To become distinguished or distinctive; to make one's self
      or itself discernible. [R.]
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            The little embryo . . . first distinguishes into a
            little knot.                          --Jer. Taylor.
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WordNet (r) 3.0 (2006):

distinguish
    v 1: mark as different; "We distinguish several kinds of maple"
         [syn: distinguish, separate, differentiate, secern,
         secernate, severalize, severalise, tell, tell
         apart]
    2: 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]
    3: be a distinctive feature, attribute, or trait; sometimes in a
       very positive sense; "His modesty distinguishes him from his
       peers" [syn: distinguish, mark, differentiate]
    4: make conspicuous or noteworthy [syn: signalize,
       signalise, distinguish]
    5: identify as in botany or biology, for example [syn:
       identify, discover, key, key out, distinguish,
       describe, name]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "distinguish":
   adorn, aggrandize, analyze, anatomize, atomize, be characteristic,
   behold, bestow honor upon, call attention to, catch sight of,
   categorize, change, characterize, chop logic, clap eyes on,
   classify, confer distinction on, contradistinguish, decide, define,
   demarcate, demark, denote, describe, descry, designate,
   desynonymize, detach, detect, determinate, determine, diagnose,
   difference, differentiate, dignify, discern, discover,
   discriminate, disengage, disequalize, disjoin, diversify, divide,
   draw the line, earmark, ennoble, erect, espy, extricate, feel,
   finger, glimpse, glorify, grace, grade, group, have, have in sight,
   hear, honor, identify, indicate, individualize, individuate, judge,
   ken, keynote, know, know again, lay eyes on, look on, look upon,
   magnify, make a distinction, make out, mark, mark off, mark out,
   mark the interface, modify, nail, note, notice, observe, part,
   particularize, peg, perceive, personalize, pick out, pick up,
   pinpoint, place, qualify, realize, recall knowledge of, recognize,
   refine a distinction, reidentify, remark, screen, screen out, see,
   segregate, select, sense, separate, set a limit, set apart,
   set off, set the pace, set the tone, sever, severalize, sieve,
   sieve out, sift, sift out, sight, signalize, single out, smell,
   sort, sort out, sound the keynote, specialize, split hairs, spot,
   spy, subdivide, sublime, subtilize, take in, taste, tell,
   tell apart, twig, uprear, vary, view, winnow, witness