Ought the chief to cool down? He's rash! (7)
I believe the answer is:
hothead
'ought the chief to cool down? he's rash' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'chief to cool down? he's rash' is the wordplay.
'chief' becomes 'head' (synonyms).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'cool down? he's rash' becomes 'hot' (I can't explain this - if you can you should give a lot more credence to this answer).
'head' after 'hot' is 'HOTHEAD'.
Can you help me to learn more?
(Other definitions for hothead that I've seen before include "Headstrong type" , "Harry Percy was one" , "Tearaway" , "Madcap" , "Person liable to get reckless impulses" .)