The Collaborative International Dictionary of English v.0.48:

Gunner \Gun"ner\, n.
   1. One who works a gun or cannon, whether on land, sea, or in
      the air; a cannoneer.
      [1913 Webster]

   2. A warrant officer in the navy having charge of the
      ordnance on a vessel.
      [1913 Webster]

   3. (Zool.)
      (a) The great northern diver or loon. See Loon.
      (b) The sea bream. [Prov. Eng. or Irish]
          [1913 Webster]

   Gunner's daughter, the gun to which men or boys were lashed
      for punishment. [Sailor's slang] --W. C. Russell.

   tail gunner (Mil.) A member of the crew of a bomber
      airplane who operates the defensive gun at the rear of the
      airplane.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

gunner
    n 1: a serviceman in the artillery [syn: artilleryman,
         cannoneer, gunner, machine gunner]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "gunner":
   Nimrod, aerial photographer, aircrew, aircrewman, archer,
   artillerist, artilleryman, avigator, bakehead, belly gunner,
   black gang, boilerman, bomb thrower, bombardier, bomber, bowman,
   bungs, cabin boy, cannoneer, carabineer, chips, commissary steward,
   complement, crack shot, crew, crew chief, dead shot, deadeye,
   deckhand, deckie, fireman, flight attendant, flight crew,
   good shot, gun, gun loader, gunman, hand, hospital steward,
   hostess, hunter, landing signalman, machine gunner, mail orderly,
   marksman, markswoman, meteorologist, musketeer, navigator, oiler,
   purser, radio operator, rifleman, roustabout, sharpshooter,
   shooter, shot, snip, sniper, snips, sparks, steward, stewardess,
   stoker, targetshooter, torpedoman, toxophilite, trapshooter, watch,
   yeoman