Shape of real bum (6)
I believe the answer is:
loafer
'bum' is the definition.
(synonyms)
'shape of real' is the wordplay.
'shape' indicates anagramming the letters.
'of'+'real'='ofreal'
'ofreal' with letters rearranged gives 'LOAFER'.
(Other definitions for loafer that I've seen before include "Fanciful baker" , "One shirking work" , "Wastrel - shoe" , "Casual footwear" , "one taking it easy" .)