Notice that is at front of university for so long (5)
I believe the answer is:
adieu
'so long' is the definition.
('adieu' can be a synonym of 'so long')
'notice that is at front of university' is the wordplay.
'notice' becomes 'ad'.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'at front of' is a charade indicator (letters next to each other).
'university' becomes 'u'.
'ad'+'ie'+'u'='ADIEU'
'for' is the link.
(Other definitions for adieu that I've seen before include "the last word in Paris" , "farewell message" , "Fare thee well!" , "12 Down" , "Farewell, Monsieur!" .)