thicket vs underwood

thicket and underwood both are nouns.

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

As nouns, underwood is a hyponym of thicket; that is, underwood is a word with a more specific, narrower meaning than thicket:

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

Other hyponyms of thicket include brake, canebrake, spinney, underbrush, undergrowth.

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