Fan calm under pressure (4)
I believe the answer is:
cool
I believe this clue is a double definition.
'fan' is the first definition.
(fan can mean to keep cool)
'calm under pressure' is the second definition.
(I've seen this in another clue)
(Other definitions for cool that I've seen before include "Free of heat; laid-back" , "Casual and confident - not heated" , "Hip - not warm" , "Super!" , "Fan" .)