Japanese brome vs bromegrass

Japanese brome and bromegrass both are nouns.

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

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

Japanese brome: grass of Mediterranean and temperate Asia
bromegrass: any of various woodland and meadow grasses of the genus Bromus; native to temperate regions

Other hypernyms of Japanese brome include brome.

Japanese brome (noun)	bromegrass (noun)
grass of Mediterranean and temperate Asia	any of various woodland and meadow grasses of the genus Bromus; native to temperate regions