Coolheadedness (5)
I believe the answer is:
poise
'coolheadedness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for poise that I've seen before include "Dignified and self-assured manner" , "Dignity; equilibrium" , "Dignity and assurance of manner" , "Grace; equilibrium" , "Elegance" .)