Crazy headgear for a hothead (6)
I believe the answer is:
madcap
'for a hothead' is the definition.
('madcap' can be a synonym of 'hothead')
'crazy headgear' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'headgear' becomes 'cap' (cap is a kind of headgear).
'mad'+'cap'='MADCAP'
(Other definitions for madcap that I've seen before include "Harum-scarum" , "Insane headgear for wildly impulsive person" , "Rash person" , "Dare-devil" , "Crazy fellow" .)