Agrostis canina vs bent-grass

Agrostis canina and bent-grass both are nouns.

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

As nouns, bent-grass is a hypernym of Agrostis canina; that is, bent-grass is a word with a broader meaning than Agrostis canina:

Agrostis canina: common grass with slender stems and narrow leaves
bent-grass: grass for pastures and lawns especially bowling and putting greens

Other hypernyms of Agrostis canina include bent, bent grass.

Agrostis canina (noun)	bent-grass (noun)
common grass with slender stems and narrow leaves	grass for pastures and lawns especially bowling and putting greens