undergrowth vs forest

undergrowth and forest both are nouns.

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

undergrowth (noun)	forest (noun)
the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest	the trees and other plants in a large densely wooded area
	land that is covered with trees and shrubs

undergrowth (verb)	forest (verb)
	establish a forest on previously unforested land