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-grass, bent.

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