yellow dock vs sour grass

yellow dock and sour grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
yellow dock	Yes	No	No	No
sour grass	Yes	No	No	No

As nouns, sour grass is a hypernym of yellow dock; that is, sour grass is a word with a broader meaning than yellow dock:

yellow dock: European dock with broad obtuse leaves and bitter rootstock common as a weed in North America
sour grass: any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine

Other hypernyms of yellow dock include dock, sorrel.

yellow dock (noun)	sour grass (noun)
European dock with broad obtuse leaves and bitter rootstock common as a weed in North America	any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine