flat coat vs priming coat

flat coat and priming coat both are nouns.

Word	Noun	Adjective	Verb	Adverb
flat coat	Yes	No	No	No
priming coat	Yes	No	No	No

As nouns, flat coat and priming coat are synonyms defined as:

flat coat and priming coat: the first or preliminary coat of paint or size applied to a surface

Other synonyms of flat coat include ground, primer, primer coat, priming, undercoat.

flat coat (noun)	priming coat (noun)
the first or preliminary coat of paint or size applied to a surface	the first or preliminary coat of paint or size applied to a surface