University with wise custom (5)
I believe the answer is:
usage
'custom' is the definition.
(I know that custom can be written as usage)
'university with wise' is the wordplay.
'university' becomes 'U' (abbreviation for university).
'with' is a charade indicator (letters next to each other).
'wise' becomes 'sage' (similar in meaning).
'u'+'sage'='USAGE'
(Other definitions for usage that I've seen before include "etiquette" , "Interest of old" , "Style of language" , "linguistic custom?" , "Terminology - custom" .)