Returned books about dress on a Russian empress (7)
I believe the answer is:
tsarina
'russian empress' is the definition.
(I've seen this before)
'returned books about dress on a' is the wordplay.
'returned' shows that the letters should be reversed in order.
'books' becomes 'NT' (New Testament).
'about' means one lot of letters goes inside another.
'dress' becomes 'sari' (sari is a kind of dress).
'on' means one lot of letters go next to another.
'nt' reversed gives 'tn'.
'tn' enclosing 'sari' is 'tsarin'.
'tsarin'+'a'='TSARINA'
(Other definitions for tsarina that I've seen before include "Nicholas's wife" , "titled lady" , "Foreign ruler" , "Catherine, say" , "aristocratic woman" .)