From Longman Dictionary of Contemporary Englishunderbrushun‧der‧brush /ˈʌndəbrʌʃ $ -ər-/ noun [uncountable] especially American EnglishHBP bushes, small trees etc growing under and around larger trees in a forest SYN undergrowth
Examples from the Corpus
underbrush• The rebels fought like demons, and under cover of the dense underbrush poured deadly volleys upon us.• Some of the plantations up north near Tay Ninh were in operation and were fairly clear of underbrush.• The tangled underbrush showed no trace of a horse's passing.• I didn't so much take cover in the underbrush, I collided with it.• We might as well clear some of the underbrush, man to man, right now, though.• A path led through the underbrush to the shanty of a woman named Mrs Fetchalub, his closest neighbor.• I'd like to get this underbrush cleaned out now. 