Old-fashioned books about university (3)
I believe the answer is:
out
'old-fashioned' is the definition.
(as opposed to 'in')
'books about university' is the wordplay.
'books' becomes 'ot' (Old Testament).
'about' indicates putting letters inside.
'university' becomes 'u' (abbreviation for university).
'ot' going around 'u' is 'OUT'.
(Other definitions for out that I've seen before include "For example, caught" , "In error" , "Not allowed - on strike" , "No longer in prison" , "Heading back to the pavilion?" .)