The Collaborative International Dictionary of English v.0.48:

pestle \pes"tle\ (p[e^]s"t'l or p[e^]s"'l; 277), n. [OE. pestel,
   OF. pestel, LL. pestellum, L. pistillum, pistillus, a
   pounder, pestle, fr. pisere, pinsere, to pound, crush, akin
   to Gr. pti`ssein, Skr. pish. Cf. Pistil.]
   1. An implement for pounding and breaking or braying
      substances in a mortar; as, to grind with a mortar and
      pestle.
      [1913 Webster]

   2. A constable's or bailiff's staff; -- so called from its
      shape. [Obs.] --Chapman.
      [1913 Webster]

   3. The leg and leg bone of an animal, especially of a pig;
      as, a pestle of pork.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

pestle \pes"tle\, v. t. & i. [imp. & p. p. Pestled; p. pr. &
   vb. n. Pestling.]
   To pound, pulverize, bray, or mix with a pestle, or as with a
   pestle; to use a pestle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pestle
    n 1: machine consisting of a heavy bar that moves vertically for
         pounding or crushing ores [syn: stamp, pestle]
    2: a heavy tool of stone or iron (usually with a flat base and a
       handle) that is used to grind and mix material (as grain or
       drugs or pigments) against a slab of stone [syn: pestle,
       muller, pounder]
    3: a club-shaped hand tool for grinding and mixing substances in
       a mortar
    v 1: grind, mash or pulverize in a mortar; "pestle the garlic"

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "pestle":
   abrade, atomize, beat, bray, brecciate, cheese grater, comminute,
   comminutor, contriturate, crumb, crumble, crush, crusher,
   disintegrate, flour, fragment, grain, granulate, granulator,
   granulize, grate, grater, grind, grind to powder, grinder,
   kominuter, levigate, levigator, mash, masher, mill, millstone,
   mortar and pestle, nutmeg grater, pound, powder, pulverize,
   pulverizer, quern, quernstone, reduce to powder, rock crusher,
   roller, scrunch, shard, shred, shredder, smash, squash,
   steamroller, triturate, triturator