Police Captain possesses a very cool head (6)
I believe the answer is:
icecap
'a very cool head' is the definition.
The definition and answer can be both natural objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'police captain possesses' is the wordplay.
'possesses' says the answer is hidden in the clue.
'ICECAP' is hidden within 'police captain'.
Can you help me to learn more?
(Other definitions for icecap that I've seen before include "Feature of polar regions" , "Area round pole" , "Permanent covering of frozen water" , "Frozen polar region" , "Permanent frozen polar cover" .)