spark plug

American  

noun

spark plugs plural

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.

---

Other Word Forms

Noun Inflected Forms

• spark plugs
  plural

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

Meanwhile, tune-ups, oil changes and spark plug replacements are now things of the past at the South Pasadena Police Department.

From Los Angeles Times • Jul. 30, 2024

There were times when a crew needed that kind of spark plug to get it revved up and firing on all cylinders.

From "The Boys in the Boat: Nine Americans and Their Epic Quest for Gold at the 1936 Berlin Olympics" by Daniel James Brown