sedge vs nut grass

sedge and nut grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
sedge	Yes	No	No	No
nut grass	Yes	No	No	No

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

sedge: grasslike or rushlike plant growing in wet places having solid stems, narrow grasslike leaves and spikelets of inconspicuous flowers
nut grass: a widely distributed perennial sedge having small edible nutlike tubers

sedge (noun)	nut grass (noun)
grasslike or rushlike plant growing in wet places having solid stems, narrow grasslike leaves and spikelets of inconspicuous flowers	a widely distributed perennial sedge having small edible nutlike tubers