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.
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            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.
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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]