The Collaborative International Dictionary of English v.0.48:

Monoceros \Mo*noc"e*ros\, n. [L., fr. Gr. ?; mo`nos alone,
   single + ke`ras horn.]
   1. A one-horned creature; a unicorn; a sea monster with one
      horn.
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            Mighty monoceroses with immeasured tails. --Spenser.
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   2. (Astron.) The Unicorn, a constellation situated to the
      east Orion.
      [1913 Webster]