Superior wise person demonstrates customary style of language (5)
I believe the answer is:
usage
'customary style of language' is the definition.
'superior wise person' is the wordplay.
'superior' becomes 'u' (I've seen this in other clues).
'wise person' becomes 'sage' (I've seen this before).
'u'+'sage'='USAGE'
'demonstrates' is the link.
(Other definitions for usage that I've seen before include "Customary practice" , "Treatment; tradition" , "Interest of old" , "Employment - practice" , "Acceptable language" .)