bristlegrass vs foxtail

bristlegrass and foxtail both are nouns.

Word	Noun	Adjective	Verb	Adverb
bristlegrass	Yes	No	No	No
foxtail	Yes	No	No	No

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

bristlegrass: 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 bristlegrass include foxtail grass.

bristlegrass (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