Finally books a quiet band (4)
I believe the answer is:
sash
'band' is the definition.
(sash is a kind of band)
'finally books a quiet' is the wordplay.
'finally' indicates one should take the final letters.
'quiet' becomes 'sh'.
The last letter of 'books' is 's'.
's'+'a'+'sh'='SASH'
(Other definitions for sash that I've seen before include "Decoration for the twelfth" , "Part of a window - decoration" , "Strip of cloth worn round the waist" , "Window frame; silk band" , "Strip of cloth - type of window" .)