Expose as a fraud (6)
I believe the answer is:
debunk
'expose as a fraud' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for debunk that I've seen before include "Disprove" , "Expose pretensions of" , "Explode pretensions, myth, of" , "Ridicule" , "Show to be false or unjustified" .)