dog grass vs couch grass

dog grass and couch grass both are nouns.

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

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

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

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

dog grass (noun)	couch 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