foxtail grass vs foxtail

foxtail grass and foxtail both are nouns.

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

As nouns, foxtail grass and foxtail are synonyms defined as:

foxtail grass and foxtail: grasses of the genera Alopecurus and Setaria having dense silky or bristly brushlike flowering spikes

foxtail grass (noun)	foxtail (noun)
grasses of the genera Alopecurus and Setaria having dense silky or bristly brushlike flowering spikes	grasses of the genera Alopecurus and Setaria having dense silky or bristly brushlike flowering spikes
ground pine thickly covered with bristly leaves; widely distributed in barren sandy or peaty moist coastal regions of eastern and southeastern United States