Definitions for underbrushˈʌn dərˌbrʌʃ
Random House Webster's College Dictionary
shrubs, saplings, low vines, etc., growing under the large trees in a wood or forest.
Origin of underbrush:
underbrush, undergrowth, underwood(noun)
the brush (small trees and bushes and ferns etc.) growing beneath taller trees in a wood or forest
The small trees and other plants that clutter the floor of a forest.
shrubs, small trees, and the like, in a wood or forest, growing beneath large trees; undergrowth