Hat for a hunter (11)
I believe the answer is:
deerstalker
'hat' is the definition.
(deerstalker is a kind of hat)
'for a hunter' is the wordplay.
'for a' becomes 'deer' (I can't justify this - if you can you should believe this answer much more).
'hunter' becomes 'stalker' (stalker is a kind of hunter).
'deer'+'stalker'='DEERSTALKER'
Can you help me to learn more?
(Other definitions for deerstalker that I've seen before include "Hunting cap" , "Sherlock Holmes' hat" , "Hunter's hat" , "Holmes's headgear" , "that Sherlock Holmes wore out" .)