Self-possession (6)
I believe the answer is:
aplomb
'self-possession' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for aplomb that I've seen before include "Pompous dignity or poise" , "Self-satisfied assurance" , "Self-satisfied poise" , "Self-satisfied dignity, complacency" , "Nonchalant confidence" .)