Coercion to turn gown round (6)
I believe the answer is:
duress
'coercion' is the definition.
(under duress means being coerced)
'turn gown round' is the wordplay.
'turn' becomes 'u' (a 'U-turn' is a kind of turn).
'gown' becomes 'dress' (gown is a kind of dress).
'round' is an insertion indicator.
'u' going within 'dress' is 'DURESS'.
'to' acts as a link.
(Other definitions for duress that I've seen before include "Pressure (involving threats)" , "Compulsion by use of force" , "Constraint, Compulsion" , "Pressure applied by druses" , "Excessive pressure" .)