couch vs flat coat

couch and flat coat both are nouns.

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

As nouns, flat coat is a hypernym of couch; that is, flat coat is a word with a broader meaning than couch:

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

Other hypernyms of couch include ground, primer, primer coat, priming, priming coat, undercoat.

couch (noun)	flat coat (noun)
an upholstered seat for more than one person	the first or preliminary coat of paint or size applied to a surface
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

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