Definition of spark plug
1
: a part that fits into the cylinder head of an internal combustion engine and carries two electrodes separated by an air gap across which the current from the ignition system discharges to form the spark for combustion
2
: one that initiates or gives impetus to an undertaking
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Merriam-Webster unabridged
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Time Traveler for spark plug
The first known use of spark plug was in 1903
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