Composure of model one's accepted (5)
I believe the answer is:
poise
'composure' is the definition.
(I know that poise is a type of composure)
'model one's accepted' is the wordplay.
'model' becomes 'pose' (model can mean to pose).
'one' becomes 'i' (Roman numeral).
'accepted' indicates putting letters inside.
'pose' enclosing 'i' is 'POISE'.
'of' acts as a link.
(Other definitions for poise that I've seen before include "Grace; equilibrium" , "Aplomb" , "Coolness and composure under strain" , "Graceful and elegant bearing in a person" , "Balance; composure" .)