rye grass vs darnel

rye grass and darnel both are nouns.

Word	Noun	Adjective	Verb	Adverb
rye grass	Yes	No	No	No
darnel	Yes	No	No	No

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

rye grass: any of several annual or perennial Eurasian grasses
darnel: weedy annual grass often occurs in grainfields and other cultivated land; seeds sometimes considered poisonous

rye grass (noun)	darnel (noun)
any of several annual or perennial Eurasian grasses	weedy annual grass often occurs in grainfields and other cultivated land; seeds sometimes considered poisonous