yardgrass vs yard grass

yardgrass and yard grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
yardgrass	Yes	No	No	No
yard grass	Yes	No	No	No

As nouns, yardgrass and yard grass are synonyms defined as:

yardgrass and yard grass: coarse annual grass having fingerlike spikes of flowers; native to Old World tropics; a naturalized weed elsewhere

Other synonyms of yardgrass include Eleusine indica, goose grass, wire grass.

yardgrass (noun)	yard grass (noun)
coarse annual grass having fingerlike spikes of flowers; native to Old World tropics; a naturalized weed elsewhere	coarse annual grass having fingerlike spikes of flowers; native to Old World tropics; a naturalized weed elsewhere