reddish brown vs copper

reddish brown and copper both are nouns.

Word	Noun	Adjective	Verb	Adverb
reddish brown	Yes	No	No	No
copper	Yes	No	Yes	No

As nouns, copper is a hyponym of reddish brown; that is, copper is a word with a more specific, narrower meaning than reddish brown:

Other hyponyms of reddish brown include brick red, copper color, Indian red.

reddish brown (noun)	copper (noun)
a shade of brown with a tinge of red	any of various small butterflies of the family Lycaenidae having coppery wings
	a reddish-brown color resembling the color of polished copper
	uncomplimentary terms for a policeman
	a copper penny
	a ductile malleable reddish-brown corrosion-resistant diamagnetic metallic element; occurs in various minerals but is the only metal that occurs abundantly in large masses; used as an electrical and thermal conductor

reddish brown (verb)	copper (verb)
	coat with a layer of copper