So long to suffer in a university (5)
I believe the answer is:
adieu
'so long' is the definition.
('adieu' can be a synonym of 'so long')
'suffer in a university' is the wordplay.
'suffer' becomes 'die' (dying is a kind of suffering).
'in' is an insertion indicator.
'university' becomes 'u'.
'a'+'u'='au'
'die' placed inside 'au' is 'ADIEU'.
'to' acts as a link.
(Other definitions for adieu that I've seen before include "Leave" , "Farewell (French)" , "Goodbye, mademoiselle" , "Parting greeting" , "Parting word" .)