sour grass vs sour dock

sour grass and sour dock both are nouns.

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

As nouns, sour dock is a hyponym of sour grass; that is, sour dock is a word with a more specific, narrower meaning than sour grass:

sour grass: any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine
sour dock: European sorrel with large slightly acidic sagittate leaves grown throughout north temperate zone for salad and spring greens

sour grass (noun)	sour dock (noun)
any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine	European sorrel with large slightly acidic sagittate leaves grown throughout north temperate zone for salad and spring greens