carpet grass vs dropseed

carpet grass and dropseed both are nouns.

Word	Noun	Adjective	Verb	Adverb
carpet grass	Yes	No	No	No
dropseed	Yes	No	No	No

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

carpet grass: grass native to West Indies but common in southern United States having tufted wiry stems often infested with a dark fungus
dropseed: a grass of the genus Sporobolus

Other hypernyms of carpet grass include drop-seed.

carpet grass (noun)	dropseed (noun)
grass native to West Indies but common in southern United States having tufted wiry stems often infested with a dark fungus	a grass of the genus Sporobolus