wood vs undergrowth

wood and undergrowth both are nouns.

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

wood (noun)	undergrowth (noun)
any wind instrument other than the brass instruments	the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest
a golf club with a long shaft used to hit long shots; originally made with a wooden head
the trees and other plants in a large densely wooded area
the hard fibrous lignified substance under the bark of trees