IPA: /ˈʌndərˌbrʌʃ/
KK: /ˈʌndərˌbrʌʃ/
A layer of small plants, shrubs, or trees that grow under larger trees in a forest, often creating a dense area that can be difficult to walk through.
The deer hid in the underbrush to avoid being seen.
Underbrush → It is formed from "under" (from Old English "under", meaning beneath or below) and "brush" (from Old French "brosse", meaning a thicket or a mass of small trees and shrubs). The word "underbrush" refers to the dense growth of shrubs and small trees that grows beneath larger trees in a forest.
Imagine the dense growth of plants that lies 'beneath' ('under') the taller trees, which is what 'underbrush' refers to.
No commonly confused words.