spark plug vs sparking plug

spark plug and sparking plug both are nouns.

Word	Noun	Adjective	Verb	Adverb
spark plug	Yes	No	No	No
sparking plug	Yes	No	No	No

As nouns, spark plug and sparking plug are synonyms defined as:

spark plug and sparking plug: electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark

Other synonyms of spark plug include plug.

spark plug (noun)	sparking plug (noun)
electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark	electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark