Cover done with falsity (7)
I believe the answer is:
overlie
'cover' is the definition.
(I've seen this in another clue)
'done with falsity' is the wordplay.
'done with' becomes 'over' (similar in meaning as in 'over and done with').
'falsity' becomes 'lie' (lie is a kind of falsity).
'over'+'lie'='OVERLIE'
(Other definitions for overlie that I've seen before include "Sleep too long, maybe" , "To cover up" , "with crushing effect" , "Sit on top of" , "Rest on top of" .)