Spinster fashions mad idol (3,4)
I believe the answer is:
old maid
'spinster' is the definition.
(synonyms)
'fashions mad idol' is the wordplay.
'fashions' indicates an anagram.
'mad'+'idol'='madidol'
'madidol' with letters rearranged gives 'OLD MAID'.
(Other definitions for old maid that I've seen before include "Singleton" , "never taken from the shelf?" , "game of cards" , "Obsolete expression for elderly unmarried woman" , "Miss" .)