spark plug

  1. an electrical device threaded into the cylinder of an internal-combustion engine to ignite the fuel mixture by producing timed sparks between electrodes
  2. Informal a person or thing that inspires, activates, or advances something

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See spark plug in American Heritage Dictionary 4

noun
  1. A device inserted in the head of an internal-combustion engine cylinder that ignites the fuel mixture by means of an electric spark.
  2. Informal One who gives life or energy to an endeavor.

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spark plug

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A. terminal B. ceramic insulation C. center electrode D. gap E. ground electrode

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spark plug

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