Clean thoroughly (5)
I believe the answer is:
scrub
'clean thoroughly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scrub that I've seen before include "Clean with hard brush and soapy water" , "something in the garden?" , "Area of dense stunted vegetation" , "Clean by rubbing really hard" , "Cancel; clean vigorously" .)