groundcover vs underwood

groundcover and underwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
groundcover	Yes	No	No	No
underwood	Yes	No	No	No

As nouns, underwood is a hypernym of groundcover; that is, underwood is a word with a broader meaning than groundcover:

groundcover: small plants other than saplings growing on a forest floor
underwood: the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest

Other hypernyms of groundcover include underbrush, undergrowth.

groundcover (noun)	underwood (noun)
small plants other than saplings growing on a forest floor	the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest
low-growing plants planted in deep shade or on a steep slope where turf is difficult to grow