pacemaker

from WordNet (r) 3.0 (2006)

pacemaker
    n 1: a leading instance in its field; "the new policy will be a
         pacesetter in community relations" [syn: {pacesetter},
         {pacemaker}]
    2: a specialized bit of heart tissue that controls the heartbeat
       [syn: {pacemaker}, {cardiac pacemaker}, {sinoatrial node},
       {SA node}]
    3: an implanted electronic device that takes over the function
       of the natural cardiac pacemaker [syn: {pacemaker},
       {artificial pacemaker}]
    4: a horse used to set the pace in racing [syn: {pacer},
       {pacemaker}, {pacesetter}]

from The Collaborative International Dictionary of English v.0.48

pacemaker \pacemaker\ n. (Physiol. & Anat.)
   1. a specialized bit of heart tissue that controls the
      heartbeat.

   Syn: cardiac pacemaker, sinoatrial node.
        [WordNet 1.5]

   2. An implanted electronic device that takes over the
      function of the natural cardiac pacemaker[1]; -- used to
      assist people whose heartbeat is irregular.

   Syn: artificial pacemaker.
        [WordNet 1.5]

   3. A horse used to set the pace in racing.

   Syn: pacer, pacesetter.
        [WordNet 1.5]