Spark plug n. In internal-combustion engines with electric ignition, a plug, screwed into the cylinder head, connected with the induction coil or magneto circuit on the outside, and used to produce a spark to ignite the fuel-air mixture in the engine.
... some conversation with him this morning," laughed Roy; "but to return to the spark plug; it's a good thing we carry ... — The Girl Aviators' Motor Butterfly • Margaret Burnham
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