"pacemaker" in the noun sense
1. pacesetter, pacemaker
a leading instance in its field
"the new policy will be a pacesetter in community relations"
2. pacemaker, cardiac pacemaker, sinoatrial node, SA node
a specialized bit of heart tissue that controls the heartbeat
3. pacemaker, artificial pacemaker
an implanted electronic device that takes over the function of the natural cardiac pacemaker
4. pacer, pacemaker, pacesetter
a horse used to set the pace in racing
Source: WordNet® (An amazing lexical database of English)
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