sparkplug

/S P AA1 R K P L AH1 G/
noun
  1. 1

    The part of an internal combustion engine which forms a high-voltage electric spark which ignites the fuel-air mixture to begin the power stroke.

  2. 2

    Someone who is a driving force in new endeavours.

Source: https://en.wiktionary.org/wiki/spark%20plug, https://en.wiktionary.org/wiki/sparkplug