Shape for rug (6)
I believe the answer is:
format
'shape' is the definition.
(I've seen this before)
'for rug' is the wordplay.
'rug' becomes 'mat' (I've seen this before).
'for'+'mat'='FORMAT'
(Other definitions for format that I've seen before include "Structure, layout" , "Way in which something is presented" , "Style or arrangement of procedure" , "General arrangement of a publication" , "magazine" .)