Royal not returning to university (9)
I believe the answer is:
princeton
'to university' is the definition.
(Princeton University is an example)
'royal not returning' is the wordplay.
'royal' becomes 'prince' (prince is a kind of royal).
'returning' says the letters should be written backwards.
'not' in reverse letter order is 'ton'.
'prince'+'ton'='PRINCETON'
(Other definitions for princeton that I've seen before include "US ivy league university" , "Early US university" , "Member of the 11 in New Jersey" , "American university" , "College" .)