velvet bent grass vs bent grass

velvet bent grass and bent grass both are nouns.

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

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

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

Other hypernyms of velvet bent grass include bent-grass, bent.

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