The Collaborative International Dictionary of English v.0.48:

Cannon \Can"non\, n.; pl. Cannons, collectively Cannon. [F.
   cannon, fr. L. canna reed, pipe, tube. See Cane.]
   1. A great gun; a piece of ordnance or artillery; a firearm
      for discharging heavy shot with great force.
      [1913 Webster]

   Note: Cannons are made of various materials, as iron, brass,
         bronze, and steel, and of various sizes and shapes with
         respect to the special service for which they are
         intended, as intended, as siege, seacoast, naval,
         field, or mountain, guns. They always aproach more or
         less nearly to a cylindrical from, being usually
         thicker toward the breech than at the muzzle. Formerly
         they were cast hollow, afterwards they were cast,
         solid, and bored out. The cannon now most in use for
         the armament of war vessels and for seacoast defense
         consists of a forged steel tube reinforced with massive
         steel rings shrunk upon it. Howitzers and mortars are
         sometimes called cannon. See Gun.
         [1913 Webster]

   2. (Mech.) A hollow cylindrical piece carried by a revolving
      shaft, on which it may, however, revolve independently.
      [1913 Webster]

   3. (Printing.) A kind of type. See Canon.
      [1913 Webster]

   Cannon ball, strictly, a round solid missile of stone or
      iron made to be fired from a cannon, but now often applied
      to a missile of any shape, whether solid or hollow, made
      for cannon. Elongated and cylindrical missiles are
      sometimes called bolts; hollow ones charged with
      explosives are properly called shells.

   Cannon bullet, a cannon ball. [Obs.]

   Cannon cracker, a fire cracker of large size.

   Cannon lock, a device for firing a cannon by a percussion
      primer.

   Cannon metal. See Gun Metal.

   Cannon pinion, the pinion on the minute hand arbor of a
      watch or clock, which drives the hand but permits it to be
      moved in setting.

   Cannon proof, impenetrable by cannon balls.

   Cannon shot.
      (a) A cannon ball.
      (b) The range of a cannon.
          [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CANNON SHOT, war. The distance which a cannon will throw a ball. 2. The
whole space of the sea, within cannon shot of the coast, is considered as
making a part of the territory; and for that reason, a vessel taken under
the cannon of a neutral fortress, is not a lawful prize. Vatt. b. 1, c. 23,
s. 289, in finem Chitt. Law of Nat. 113; Mart. Law of Nat. b. 8, c. 6, s. 6;
3 Rob. Adm. Rep. 102, 336; 5 Id. 373; 3 Hagg. Adm. R. 257. This part of the
sea being considered as part of the adjacent territory, (q.v.) it follows
that magistrates can cause the orders of their governments to be executed
there. Three miles is considered as the greatest distance that the force of
gunpowder can carry a bomb or a ball. Azun. far. Law, part 2, c. 2, art. 2,
Sec. 15; Bouch. Inst. n. 1848. The anonymous author of the poem, Della
Natura, lib. 5, expresses this idea in the following lines: Tanto slavanza
in mar questo dominio, Quant esser puo d'antemurale e guardia, Fin dove puo
da terra in mar vibrandosi Correr di cavo bronzo acceso fulinine. Far as the
sovereign can defend his sway, Extends his empire o'er the watery way; The
shot sent thundering to the liquid plain, Assigns the limits of his just
domain. Vide League.