The Collaborative International Dictionary of English v.0.48:

Gun \Gun\ (g[u^]n), n. [OE. gonne, gunne; of uncertain origin;
   cf. Ir., Gael., & LL. gunna, W. gum; possibly (like cannon)
   fr. L. canna reed, tube; or abbreviated fr. OF. mangonnel, E.
   mangonel, a machine for hurling stones.]
   1. A weapon which throws or propels a missile to a distance;
      any firearm or instrument for throwing projectiles,
      consisting of a tube or barrel closed at one end, in which
      the projectile is placed, with an explosive charge (such
      as guncotton or gunpowder) behind, which is ignited by
      various means. Pistols, rifles, carbines, muskets, and
      fowling pieces are smaller guns, for hand use, and are
      called small arms. Larger guns are called cannon,
      ordnance, fieldpieces, carronades, howitzers, etc.
      See these terms in the Vocabulary.
      [1913 Webster]

            As swift as a pellet out of a gunne
            When fire is in the powder runne.     --Chaucer.
      [1913 Webster]

            The word gun was in use in England for an engine to
            cast a thing from a man long before there was any
            gunpowder found out.                  --Selden.
      [1913 Webster]

   2. (Mil.) A piece of heavy ordnance; in a restricted sense, a
      cannon.
      [1913 Webster]

   3. pl. (Naut.) Violent blasts of wind.
      [1913 Webster]

   Note: Guns are classified, according to their construction or
         manner of loading as rifled or smoothbore,
         breech-loading or muzzle-loading, cast or
         built-up guns; or according to their use, as field,
         mountain, prairie, seacoast, and siege guns.
         [1913 Webster]

   Armstrong gun, a wrought iron breech-loading cannon named
      after its English inventor, Sir William Armstrong.

   Big gun or Great gun, a piece of heavy ordnance; hence
      (Fig.), a person superior in any way; as, bring in the big
      guns to tackle the problem.

   Gun barrel, the barrel or tube of a gun.

   Gun carriage, the carriage on which a gun is mounted or
      moved.

   Gun cotton (Chem.), a general name for a series of
      explosive nitric ethers of cellulose, obtained by steeping
      cotton in nitric and sulphuric acids. Although there are
      formed substances containing nitric acid radicals, yet the
      results exactly resemble ordinary cotton in appearance. It
      burns without ash, with explosion if confined, but quietly
      and harmlessly if free and open, and in small quantity.
      Specifically, the lower nitrates of cellulose which are
      insoluble in ether and alcohol in distinction from the
      highest (pyroxylin) which is soluble. See Pyroxylin, and
      cf. Xyloidin. The gun cottons are used for blasting and
      somewhat in gunnery: for making celluloid when compounded
      with camphor; and the soluble variety (pyroxylin) for
      making collodion. See Celluloid, and Collodion. Gun
      cotton is frequenty but improperly called
      nitrocellulose. It is not a nitro compound, but an ester
      of nitric acid.

   Gun deck. See under Deck.

   Gun fire, the time at which the morning or the evening gun
      is fired.

   Gun metal, a bronze, ordinarily composed of nine parts of
      copper and one of tin, used for cannon, etc. The name is
      also given to certain strong mixtures of cast iron.

   Gun port (Naut.), an opening in a ship through which a
      cannon's muzzle is run out for firing.

   Gun tackle (Naut.), the blocks and pulleys affixed to the
      side of a ship, by which a gun carriage is run to and from
      the gun port.

   Gun tackle purchase (Naut.), a tackle composed of two
      single blocks and a fall. --Totten.

   Krupp gun, a wrought steel breech-loading cannon, named
      after its German inventor, Herr Krupp.

   Machine gun, a breech-loading gun or a group of such guns,
      mounted on a carriage or other holder, and having a
      reservoir containing cartridges which are loaded into the
      gun or guns and fired in rapid succession. In earlier
      models, such as the Gatling gun, the cartridges were
      loaded by machinery operated by turning a crank. In modern
      versions the loading of cartidges is accomplished by
      levers operated by the recoil of the explosion driving the
      bullet, or by the pressure of gas within the barrel.
      Several hundred shots can be fired in a minute by such
      weapons, with accurate aim. The Gatling gun, Gardner
      gun, Hotchkiss gun, and Nordenfelt gun, named for
      their inventors, and the French mitrailleuse, are
      machine guns.

   To blow great guns (Naut.), to blow a gale. See Gun, n.,
      3.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Deck \Deck\, n. [D. dek. See Deck, v.]
   1. The floorlike covering of the horizontal sections, or
      compartments, of a ship. Small vessels have only one deck;
      larger ships have two or three decks.
      [1913 Webster]

   Note: The following are the more common names of the decks of
         vessels having more than one.
         [1913 Webster]

   Berth deck (Navy), a deck next below the gun deck, where
      the hammocks of the crew are swung.

   Boiler deck (River Steamers), the deck on which the boilers
      are placed.

   Flush deck, any continuous, unbroken deck from stem to
      stern.

   Gun deck (Navy), a deck below the spar deck, on which the
      ship's guns are carried. If there are two gun decks, the
      upper one is called the main deck, the lower, the lower
      gun deck; if there are three, one is called the middle gun
      deck.

   Half-deck, that portion of the deck next below the spar
      deck which is between the mainmast and the cabin.

   Hurricane deck (River Steamers, etc.), the upper deck,
      usually a light deck, erected above the frame of the hull.


   Orlop deck, the deck or part of a deck where the cables are
      stowed, usually below the water line.

   Poop deck, the deck forming the roof of a poop or poop
      cabin, built on the upper deck and extending from the
      mizzenmast aft.

   Quarter-deck, the part of the upper deck abaft the
      mainmast, including the poop deck when there is one.

   Spar deck.
      (a) Same as the upper deck.
      (b) Sometimes a light deck fitted over the upper deck.

   Upper deck, the highest deck of the hull, extending from
      stem to stern.
      [1913 Webster]

   2. (arch.) The upper part or top of a mansard roof or curb
      roof when made nearly flat.
      [1913 Webster]

   3. (Railroad) The roof of a passenger car.
      [1913 Webster]

   4. A pack or set of playing cards.
      [1913 Webster]

            The king was slyly fingered from the deck. --Shak.
      [1913 Webster]

   5. A heap or store. [Obs.]
      [1913 Webster]

            Who . . . hath such trinkets
            Ready in the deck.                    --Massinger.
      [1913 Webster]

   6. (A["e]ronautics) A main a["e]roplane surface, esp. of a
      biplane or multiplane.
      [Webster 1913 Suppl.]

   7. the portion of a bridge which serves as the roadway.
      [PJC]

   8. a flat platform adjacent to a house, usually without a
      roof; -- it is typically used for relaxing out of doors,
      outdoor cooking, or entertaining guests.
      [PJC]

   Between decks. See under Between.

   Deck bridge (Railroad Engineering), a bridge which carries
      the track upon the upper chords; -- distinguished from a
      through bridge, which carries the track upon the lower
      chords, between the girders.

   Deck curb (Arch.), a curb supporting a deck in roof
      construction.

   Deck floor (Arch.), a floor which serves also as a roof, as
      of a belfry or balcony.

   Deck hand, a sailor hired to help on the vessel's deck, but
      not expected to go aloft.

   Deck molding (Arch.), the molded finish of the edge of a
      deck, making the junction with the lower slope of the
      roof.

   Deck roof (Arch.), a nearly flat roof which is not
      surmounted by parapet walls.

   Deck transom (Shipbuilding), the transom into which the
      deck is framed.

   To clear the decks (Naut.), to remove every unnecessary
      incumbrance in preparation for battle; to prepare for
      action.

   To sweep the deck (Card Playing), to clear off all the
      stakes on the table by winning them.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gun deck
    n 1: formerly any deck other than the weather deck having
         cannons from end to end