Idiot wants 150 books (4)
I believe the answer is:
clot
'idiot' is the definition.
(thesaurus)
'150 books' is the wordplay.
'150' becomes 'cl'.
'books' becomes 'ot' (Old Testament).
'cl'+'ot'='CLOT'
'wants' is the link.
(Other definitions for clot that I've seen before include "Fool; solidified blood" , "Thick lump - thick person" , "Twit; blood problem" , "Coagulate -- 1 across person" , "Stupid person - lump of blood" .)