spark plug

American  

noun

1. a device designed to fit in each cylinder of a gasoline-powered internal-combustion engine and to produce the electric spark for igniting the mixture of gasoline and air.

2. Informal. a person who leads, inspires, or animates a group.

---

spark plug British  

noun

1. another name for sparking plug

---

spark plug Scientific  

1. A device in the cylinder head of an internal-combustion engine that ignites the fuel mixture by means of an electric spark. Spark plugs consist of two electrodes that are separated by an insulator except at their tips. When high voltage electricity is fed to one electrode, it jumps across the gap from one tip to the other as a spark. The voltage required to generate a spark is directly proportional to the size of the gap; in a car engine it is about 18,000 volts.

---

Etymology

Origin of spark plug

First recorded in 1900–05

Example Sentences

The spark plug ignites a fuel-air mix, causing the rotor to turn a shaft, creating motion.

From The Wall Street Journal • Apr. 24, 2026

The wind-down of those businesses, including aftermarket parts maker Cardone and spark plug manufacturer Autolite, comes in addition to the layoffs announced Monday.

From The Wall Street Journal • Feb. 23, 2026

That caused a short-circuit and "arcing" - electric sparks like those in a spark plug - which resulted in a "catastrophic failure".

From BBC • Jul. 2, 2025

Both players serve important roles in the lineup, Freeman as a run-producer behind Ohtani and Mookie Betts, Rojas as a bottom-of-the-lineup spark plug who was batting almost .300 until a few weeks ago.

From Los Angeles Times • Sep. 30, 2024

As Edwin and Garvey crawled into the aluminum skiff, Cole called, “Don’t forget to put the spark plug back in.”

From "Touching Spirit Bear" by Ben Mikaelsen