couch grass vs dog grass

couch grass and dog grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
couch grass	Yes	No	No	No
dog grass	Yes	No	No	No

As nouns, couch grass and dog grass are synonyms defined as:

couch grass and dog grass: European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed

Other synonyms of couch grass include Agropyron repens, quack grass, quackgrass, quick grass, witch grass, witchgrass.

couch grass (noun)	dog grass (noun)
European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed	European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed