Set of eight books about cold empty economist (5)
I believe the answer is:
octet
'set of eight' is the definition.
(I've seen this before)
'books about cold empty economist' is the wordplay.
'books' becomes 'ot' (Old Testament).
'about' means one lot of letters goes inside another.
'cold' becomes 'c' (eg on taps).
'empty' says to hollow out the word (remove centre letters).
'economist' with its centre taken out is 'et'.
'ot' placed around 'c' is 'oct'.
'oct'+'et'='OCTET'
(Other definitions for octet that I've seen before include "Work for eight players" , "Group of eight players" , "Eightsome" , "Group that plays" , "Piece for eight players" .)