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
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Who Knew?
-
- What is a ruelle?

Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
Spell words. Make bears.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Words at Play
Ask the Editors
Share spark plug
Time Traveler for spark plug
The first known use of spark plug was in 1903
See more words from the same year