underbrush vs coppice

underbrush and coppice both are nouns.

Word	Noun	Adjective	Verb	Adverb
underbrush	Yes	No	No	No
coppice	Yes	No	No	No

As nouns, coppice is a hypernym of underbrush; that is, coppice is a word with a broader meaning than underbrush:

underbrush: the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest
coppice: a dense growth of bushes

Other hypernyms of underbrush include brush, brushwood, copse, thicket.

underbrush (noun)	coppice (noun)
the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest	a dense growth of bushes