quack grass vs wheatgrass

quack grass and wheatgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
quack grass	Yes	No	No	No
wheatgrass	Yes	No	No	No

As nouns, wheatgrass is a hypernym of quack grass; that is, wheatgrass is a word with a broader meaning than quack grass:

quack grass: European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed
wheatgrass: a grass of the genus Agropyron

Other hypernyms of quack grass include wheat-grass.

quack grass (noun)	wheatgrass (noun)
European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed	a grass of the genus Agropyron