Indian millet vs rice grass

Indian millet and rice grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Indian millet	Yes	No	No	No
rice grass	Yes	No	No	No

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

Indian millet: valuable forage grass of dry upland areas and plains of western North America to northern Mexico
rice grass: any grass of the genus Oryzopsis

Other hypernyms of Indian millet include ricegrass.

Indian millet (noun)	rice grass (noun)
sorghums of dry regions of Asia and North Africa	any grass of the genus Oryzopsis
valuable forage grass of dry upland areas and plains of western North America to northern Mexico