downy brome vs bromegrass

downy brome and bromegrass both are nouns.

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

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

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

Other hypernyms of downy brome include brome.

downy brome (noun)	bromegrass (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