spark plug

• sparkplug
• sparking plug (dated)

spark plug (plural spark plugs)

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.
   • 1919 January 1, Practical hints on running a gas engine, United States Department of Agriculture:

     With all engines using spark plugs it is comparatively easy to ascertain whether the ignition system is working properly.

2. (figuratively) Someone who is a driving force in new endeavours.

   Synonyms: straw that stirs the drink, catalyst, instigator, mover and shaker, stimulus

   • 2003, Growing for Market: News and Ideas for Market Gardeners:

     Steve Pincus, a Madison-area farmer who sells produce to L'Etoile, says admiringly of Odessa: "She's a spark plug. She's out there speaking out about sustainable agriculture and local food."