The Collaborative International Dictionary of English v.0.48:

Counter tenor \Coun"ter ten`or\ (t?n`?r). [OF. contreteneur. Cf.
   Contratenor, and see Tenor a part in music.] (Mus.)
   One of the middle parts in music, between the tenor and the
   treble; high tenor.
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   Counter-tenor clef (Mus.), the C clef when placed on the
      third line; -- also called alto clef.
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The Collaborative International Dictionary of English v.0.48:

Counter \Coun"ter\, n. [See Counter, adv., Contra.]
   1. (Naut.) The after part of a vessel's body, from the water
      line to the stern, -- below and somewhat forward of the
      stern proper.
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   2. (Mus.) Same as Contra. Formerly used to designate any
      under part which served for contrast to a principal part,
      but now used as equivalent to counter tenor.
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   3. (Far.) The breast, or that part of a horse between the
      shoulders and under the neck.
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   4. The back leather or heel part of a boot.
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