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}).