Get rid of the undergrowth (5)
I believe the answer is:
scrub
This clue is a double definition.
'get rid of' is the first definition.
(scrub can mean to cancel or erase)
'undergrowth' is the second definition.
(scrub can mean undergrowth or vegetation)
'the' acts as a link.
(Other definitions for scrub that I've seen before include "Clean by rubbing really hard" , "something in the garden?" , "Curbs (anag.)" , "Clean with hard brush and soapy water" , "Clean, low vegetation" .)