underwood vs underbrush

underwood and underbrush both are nouns.

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

As nouns, underwood and underbrush are synonyms defined as:

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

Other synonyms of underwood include undergrowth.

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