bristle grass vs foxtail

bristle grass and foxtail both are nouns.

Word	Noun	Adjective	Verb	Adverb
bristle grass	Yes	No	No	No
foxtail	Yes	No	No	No

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

bristle grass: grasses of grasslands and woodlands having large gracefully arching spikes with long bristles beneath each spikelet
foxtail: grasses of the genera Alopecurus and Setaria having dense silky or bristly brushlike flowering spikes

Other hypernyms of bristle grass include foxtail grass.

bristle grass (noun)	foxtail (noun)
grasses of grasslands and woodlands having large gracefully arching spikes with long bristles beneath each spikelet	grasses of the genera Alopecurus and Setaria having dense silky or bristly brushlike flowering spikes