Muse a long time -- and return books (5)
I believe the answer is:
erato
'muse' is the definition.
(Erato is an example)
'a long time and return books' is the wordplay.
'a long time' becomes 'era' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'return' says the letters should be written in reverse.
'books' becomes 'ot' (Old Testament).
'ot' back-to-front is 'to'.
'era'+'to'='ERATO'
(Other definitions for erato that I've seen before include "Source of poetic inspiration" , "daughter of Zeus" , "poetic patroness" , "Greek muse - orate (anag)" , "Clio's sister" .)