Cool-headed (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
sane
'cool-headed' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sane that I've seen before include "Mentally sound" , "Identical" , "Healthy in mind" , "In full possession of mental faculties" , "Reasonable" .)