flat coat vs couch

flat coat and couch both are nouns.

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

As nouns, couch is a hyponym of flat coat; that is, couch is a word with a more specific, narrower meaning than flat coat:

flat coat: the first or preliminary coat of paint or size applied to a surface
couch: a flat coat of paint or varnish used by artists as a primer

flat coat (noun)	couch (noun)
the first or preliminary coat of paint or size applied to a surface	an upholstered seat for more than one person
	a narrow bed on which a patient lies during psychiatric or psychoanalytic treatment
	a flat coat of paint or varnish used by artists as a primer

flat coat (verb)	couch (verb)
	formulate in a particular style or language