brownish vs brown

brownish is not a noun while brown is a noun.

Word	Noun	Adjective	Verb	Adverb
brownish	No	Yes	No	No
brown	Yes	Yes	Yes	No

As adjectives, brownish and brown are synonyms defined as:

Other synonyms of brownish include chocolate-brown, dark-brown.

brownish (noun)	brown (noun)
	an orange of low brightness and saturation

brownish (adjective)	brown (adjective)
of a color similar to that of wood or earth	(of skin) deeply suntanned
	of a color similar to that of wood or earth

brownish (verb)	brown (verb)
	fry in a pan until it changes color
	make brown in color