bent-grass vs bent grass

bent-grass and bent grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
bent-grass	Yes	No	No	No
bent grass	Yes	No	No	No

As nouns, bent-grass and bent grass are synonyms defined as:

bent-grass and bent grass: grass for pastures and lawns especially bowling and putting greens

Other synonyms of bent-grass include bent.

bent-grass (noun)	bent grass (noun)
grass for pastures and lawns especially bowling and putting greens	grass for pastures and lawns especially bowling and putting greens