Turn on wise man for choice of words (5)
I believe the answer is:
usage
'choice of words' is the definition.
(I've seen this in another clue)
'turn on wise man' is the wordplay.
'turn' becomes 'U' (a 'U-turn' is a kind of turn).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'wise man' becomes 'sage' (sage is a kind of wise man).
'u'+'sage'='USAGE'
'for' acts as a link.
(Other definitions for usage that I've seen before include "Habit" , "Treatment, practice" , "linguistic custom?" , "Established custom" , "Terminology - custom" .)