dropseed vs smut grass

dropseed and smut grass both are nouns.

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

As nouns, smut grass is a hyponym of dropseed; that is, smut grass is a word with a more specific, narrower meaning than dropseed:

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

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