n.; pl.Horsemen1. A rider on horseback; one skilled in the management of horses; a mounted man. [ 1913 Webster ]
2. (Mil.) A mounted soldier; a cavalryman. [ 1913 Webster ]
3. (Zool.) (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 (Eques lanceolatus). [ 1913 Webster ]