The Collaborative International Dictionary of English v.0.48:

Canister \Can"is*ter\ (k[a^]n"[i^]s*t[~e]r), n. [L. canistrum a
   basket woven from reeds Gr. ?, fr. ka`nh, ka`nna reed; cf. F.
   canistre. See Cane, and Canaster.]
   1. A small basket of rushes, reeds, or willow twigs, etc.
      [1913 Webster]

   2. A small box or case for holding tea, coffee, etc.
      [1913 Webster]

   3. (Mil.) A kind of case shot for cannon, in which a number
      of lead or iron balls in layers are inclosed in a case
      fitting the gun; -- called also canister shot.
      [1913 Webster]

WordNet (r) 3.0 (2006):

canister shot
    n 1: a metallic cylinder packed with shot and used as ammunition
         in a firearm [syn: case shot, canister, canister
         shot]