United by wise tradition (5)
I believe the answer is:
usage
'tradition' is the definition.
(I've seen this in another clue)
'united by wise' is the wordplay.
'united' becomes 'U' (abbreviation).
'by' 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 "Way of employing" , "Terminology - custom" , "Treatment; tradition" , "Custom - treatment" , "Utilisation" .)