The Collaborative International Dictionary of English v.0.48:

Marksman \Marks"man\, n.; pl. Marksmen. [Earlier markman; mark
   + man.]
   1. One skillful to hit a mark with a missile; one who shoots
      well. especially with a pistol or rifle.
      [1913 Webster +PJC]

   2. (Law) One who makes his mark, instead of writing his name,
      in signing documents. --Burrill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

marksman
    n 1: someone skilled in shooting [syn: marksman,
         sharpshooter, crack shot]