Do away with — undergrowth (5)
I believe the answer is:
scrub
I believe this clue is a double definition.
'do away with' is the first definition.
(I've seen this before)
'undergrowth' is the second definition.
(scrub can mean undergrowth or vegetation)
(Other definitions for scrub that I've seen before include "Rub hard with a brush" , "Drop" , "Cancel (colloq)" , "Get rid of" , "Rub hard; brushwood" .)