copse vs undergrowth

copse and undergrowth both are nouns.

Word	Noun	Adjective	Verb	Adverb
copse	Yes	No	No	No
undergrowth	Yes	No	No	No

As nouns, undergrowth is a hyponym of copse; that is, undergrowth is a word with a more specific, narrower meaning than copse:

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

Other hyponyms of copse include brake, canebrake, spinney, underbrush, underwood.

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