darnel vs rye grass

darnel and rye grass both are nouns.

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

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

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

Other hypernyms of darnel include ryegrass.

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