rice vs brown rice

rice and brown rice both are nouns.

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

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

Other hyponyms of rice include polished rice, white rice, paddy.

rice (noun)	brown rice (noun)
grains used as food either unpolished or more often polished	unpolished rice retaining the yellowish-brown outer layer
annual or perennial rhizomatous marsh grasses; seed used for food; straw used for paper

rice (verb)	brown rice (verb)
sieve so that it becomes the consistency of rice