spark plug

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.

Origin:
1900–05

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2013.
Cite This Source Link To spark plug
Collins
World English Dictionary
spark plug
 
n
another name for sparking plug

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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00:10
Spark plug is always a great word to know.
So is interrobang. Does it mean:
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.
an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.
American Heritage
Science Dictionary
spark plug  


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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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
Cite This Source
Example sentences
When the piston returns upward in the compression cycle, the spark plug emits a
  spark to ignite the fuel-air mixture.
In a spark-ignition engine, the mixture is ignited by a spark from the spark
  plug, releasing heat.
The fuel is directed straight at the spark plug, rather than at the cylinder
  wall.
If spark plug is wet with fuel, the engine could be flooded.
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