feathertop vs reed grass

feathertop and reed grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
feathertop	Yes	No	No	No
reed grass	Yes	No	No	No

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

feathertop: a variety of reed grass
reed grass: any of various tall perennial grasses of the genus Calamagrostis having feathery plumes; natives of marshland fens and wet woodlands of temperate Northern Hemisphere

feathertop (noun)	reed grass (noun)
northeastern tropical African plant having feathery panicles	any of various tall perennial grasses of the genus Calamagrostis having feathery plumes; natives of marshland fens and wet woodlands of temperate Northern Hemisphere
a variety of reed grass