underbrush vs underwood

underbrush and underwood both are nouns.

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

As nouns, underbrush and underwood are synonyms defined as:

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

Other synonyms of underbrush include undergrowth.

underbrush (noun)	underwood (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