dog grass vs witch grass

dog grass and witch grass both are nouns.

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

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

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

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

dog grass (noun)	witch grass (noun)
European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed	North American grass with slender brushy panicles; often a weed on cultivated land
	European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed