Such sinister humour as a gang leader permits? (7)
I believe the answer is:
gallows
'such sinister humour' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'a gang leader permits?' is the wordplay.
'leader' says to take the initial letters.
'permits?' becomes 'allows' ('allow' can be a synonym of 'permit').
The first letter of 'gang' is 'g'.
'g'+'allows'='GALLOWS'
'as' is the link.
Can you help me to learn more?
(Other definitions for gallows that I've seen before include "Black comedy or jokes" , "Frame for hanging" , "Place of execution" , "suspender" , "tree" .)