downy bromegrass vs brome

downy bromegrass and brome both are nouns.

Word	Noun	Adjective	Verb	Adverb
downy bromegrass	Yes	No	No	No
brome	Yes	No	No	No

As nouns, brome is a hypernym of downy bromegrass; that is, brome is a word with a broader meaning than downy bromegrass:

downy bromegrass: annual or winter annual grass with softly hairy leaves of the Mediterranean
brome: any of various woodland and meadow grasses of the genus Bromus; native to temperate regions

Other hypernyms of downy bromegrass include bromegrass.

downy bromegrass (noun)	brome (noun)
annual or winter annual grass with softly hairy leaves of the Mediterranean	any of various woodland and meadow grasses of the genus Bromus; native to temperate regions