Clear the flat (5)
I believe the answer is:
plain
This clue is a double definition.
'clear' is the first definition.
(similar in meaning)
'flat' is the second definition.
(I've seen this in another clue)
'the' acts as a link.
(Other definitions for plain that I've seen before include "not attractive" , "Straightforward" , "Clear - open - grassland" , "Unprepossessing" , "Undecorated; flat area" .)