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"