Superior and wise custom? (5)
I believe the answer is:
usage
'custom?' is the definition.
(synonyms)
'superior and wise' is the wordplay.
'superior' becomes 'U' (U can mean upper-class, as in U and non-U speech).
'and' 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 "Interest of old" , "Habitual custom" , "management" , "Utilisation" , "Habit" .)