yard grass vs yardgrass

yard grass and yardgrass both are nouns.

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

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

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

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

yard grass (noun)	yardgrass (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