Source : Webster's Revised Unabridged Dictionary (1913)

Horseman \Horse"man\, n.; pl. {Horsemen}.
   1. A rider on horseback; one skilled in the management of
      horses; a mounted man.

   2. (Mil.) A mounted soldier; a cavalryman.

   3. (Zo["o]l.)
      (a) A land crab of the genus {Ocypoda}, living on the
          coast of Brazil and the West Indies, noted for running
          very swiftly.
      (b) A West Indian fish of the genus {Eques}, as the
          light-horseman ({E. lanceolatus}).