Learned custom abandoned by university (4)
I believe the answer is:
sage
'learned' is the definition.
(thesaurus)
'custom abandoned by university' is the wordplay.
'custom' becomes 'usage' ('usage' can be a synonym of 'custom').
'abandoned by' indicates named letters should be taken away.
'university' becomes 'u'.
'usage' with 'u' removed is 'SAGE'.
(Other definitions for sage that I've seen before include "Velvety-leaved herb" , "Clever" , "Herb used in cooking" , "Culinary herb" , "Fragrant herb or wise man" .)