Thug’s bonnet (4)
I believe the answer is:
hood
I believe this is a double definition.
'thug's' is the first definition.
(synonyms)
'bonnet' is the second definition.
(synonyms)
(Other definitions for hood that I've seen before include "Cover < the upper part < of tough" , "Capital cover" , "academic garment" , "this could provide cover" , "Cover - American gangster - Robin?" .)