Books about single composition (5)
I believe the answer is:
nonet
'composition' is the definition.
(I know that nonet is a type of composition)
'books about single' is the wordplay.
'books' becomes 'NT' (New Testament).
'about' means one lot of letters goes inside another.
'single' becomes 'one' (a single thing - only one).
'nt' going around 'one' is 'NONET'.
(Other definitions for nonet that I've seen before include "Piece of music for nine" , "Piece for nine performers" , "small band" , "Piece for nine players" , "Composition for nine voices" .)