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.
... be pushed off easy, I don't hurry about tellin' him so. Instead I climbs aboard and develops an idea. You see, when I was out with Eb Westcott in his lobster boat the day before I'd noticed him stop the engine just by jerkin' a little wire off the spark plug. Here was a whole bunch of wires, though. Wouldn't do to unhitch 'em all. But along the inside of the boat is a little box affair that they all lead into, with one big wire leadin' out. Looked kind of businesslike, that one did. I unhitches it gentle and drapes it over a nearby screwhead. ... — On With Torchy • Sewell Ford