Edges of double bed cut down to size (6)
I believe the answer is:
'cut down to size' is the definition.
(debunk can mean to discredit or expose)
'edges of double bed' is the wordplay.
'edges of' means to remove the middle letters.
'bed' becomes 'bunk' (bunk is a kind of bed).
'double' with its centre removed is 'de'.
(Other definitions for debunk that I've seen before include "Show to be false or unjustified", "Explode pretensions, myth, of", "Show to be exaggerated or false, claim or theory", "Reveal as false, show up", "Expose false claims".)