Theatrical male in type of headgear (4)
I believe the answer is:
camp
'theatrical' is the definition.
(thesaurus)
'male in type of headgear' is the wordplay.
'male' becomes 'm' (common abbreviation).
'in' is an insertion indicator.
'type of headgear' becomes 'cap'.
'm' going inside 'cap' is 'CAMP'.
(Other definitions for camp that I've seen before include "Military installation < affected" , "holiday venue" , "holiday location" , "Affected, artificial" , "David, for example" .)