Self-restraint in fashion allowance (10)
I believe the answer is:
moderation
'self-restraint' is the definition.
(I've seen this before)
'fashion allowance' is the wordplay.
'fashion' becomes 'mode' ('mode' can be a synonym of 'fashion').
'allowance' becomes 'ration' (I've seen this before).
'mode'+'ration'='MODERATION'
'in' acts as a link.
(Other definitions for moderation that I've seen before include "Avoidance of extremes" , "restraint" , "self-control" , "self-restraint" , "avoids extremes" .)