They leave old English books outside university (6)
I believe the answer is:
exeunt
'they leave' is the definition.
(stage direction meaning a group leaves the stage)
'old english books outside university' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'english' becomes 'e' (abbreviation).
'books' becomes 'NT' (abbreviation for New Testament).
'outside' is an insertion indicator.
'university' becomes 'u' (abbreviation for university).
'e'+'nt'='ent'
'ent' going around 'u' is 'eunt'.
'ex'+'eunt'='EXEUNT'
(Other definitions for exeunt that I've seen before include "(Actors) leave stage" , "More than one exit?" , "Trivial details" , "Stage direction to a group of actors (Latin)" , "Stage direction (Latin, they go out)" .)