Pressure's socially acceptable wearing frock (6)
I believe the answer is:
duress
'pressure's' is the definition.
(thesaurus)
'socially acceptable wearing frock' is the wordplay.
'socially acceptable' becomes 'u'.
'wearing' is an insertion indicator.
'frock' becomes 'dress' ('dress' can be a synonym of 'frock').
'u' placed into 'dress' is 'DURESS'.
(Other definitions for duress that I've seen before include "Constraint, coercion" , "Compulsion by use of force" , "Constraint, force" , "Threats, violence, etc, used in coercion" , "Coercion, pressure" .)