rice grass vs cereal

rice grass and cereal both are nouns.

Word	Noun	Adjective	Verb	Adverb
rice grass	Yes	No	No	No
cereal	Yes	Yes	No	No

As nouns, cereal is a hypernym of rice grass; that is, cereal is a word with a broader meaning than rice grass:

rice grass: any grass of the genus Oryzopsis
cereal: grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

Other hypernyms of rice grass include cereal grass.

rice grass (noun)	cereal (noun)
any grass of the genus Oryzopsis	a breakfast food prepared from grain
	foodstuff prepared from the starchy grains of cereal grasses
	grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

rice grass (adjective)	cereal (adjective)
	made of grain or relating to grain or the plants that produce it