old witch grass vs witchgrass

old witch grass and witchgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
old witch grass	Yes	No	No	No
witchgrass	Yes	No	No	No

As nouns, old witch grass and witchgrass are synonyms defined as:

old witch grass and witchgrass: North American grass with slender brushy panicles; often a weed on cultivated land

Other synonyms of old witch grass include old witchgrass, Panicum capillare, tumble grass, witch grass.

old witch grass (noun)	witchgrass (noun)
North American grass with slender brushy panicles; often a weed on cultivated land	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