Leave out books about Military Intelligence (4)
I believe the answer is:
omit
'leave out' is the definition.
(I know that leave out can be written as omit)
'books about military intelligence' is the wordplay.
'books' becomes 'OT' (abbreviation for Old Testament).
'about' means one lot of letters goes inside another.
'military intelligence' becomes 'MI' (as in MI5 or MI6 - British military intelligence).
'ot' going around 'mi' is 'OMIT'.
(Other definitions for omit that I've seen before include "Fail (to do something)" , "Exclude - neglect" , "Exclude; forget to include" , "Disregard" , "Don't include" .)