Stylish signature finally on a set of books (7)
I believe the answer is:
elegant
'stylish' is the definition.
(both can mean fancy or ornate)
'signature finally on a set of books' is the wordplay.
'finally' indicates one should take the final letters.
'on' becomes 'leg' (cricket term, fielding positions).
'set of books' becomes 'NT' (New Testament).
The final letter of 'signature' is 'e'.
'e'+'leg'+'a'+'nt'='ELEGANT'
(Other definitions for elegant that I've seen before include "Polished" , "Teen gal (anag.)" , "Debonair, stylishly dressed" , "Modish" , "Tasteful and refined in appearance" .)