Socially acceptable and wise custom (5)
I believe the answer is:
usage
'custom' is the definition.
('usage' can be a synonym of 'custom')
'socially acceptable and wise' is the wordplay.
'socially acceptable' becomes 'u'.
'and' is a charade indicator (letters next to each other).
'wise' becomes 'sage' ('sage' can be similar in meaning to 'wise').
'u'+'sage'='USAGE'
(Other definitions for usage that I've seen before include "phraseology" , "Custom; practice" , "Convention" , "Way of treating" , "Usual practice" .)