Rogue content in spiked headwear (4)
I believe the answer is:
kepi
'headwear' is the definition.
(type of military cap)
'rogue content in spiked' is the wordplay.
'rogue' becomes 'kep' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'content in' means to look at the middle letters.
'spiked' becomes 'fortified' ('fortify' can be a synonym of 'spike').
The middle of 'fortified' is 'i'.
'kep'+'i'='KEPI'
Can you help me to learn more?
(Other definitions for kepi that I've seen before include "French military cap" , "Flat-topped military cap" , "French military headgear" , "French military hat" , "What French soldier may assume" .)