He has absolute control of the French drug (6)
I believe the answer is:
despot
'he has absolute control' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'of the french drug' is the wordplay.
'of the french' becomes 'des' ('of the' in French).
'drug' becomes 'pot' (slang term for cannabis).
'des'+'pot'='DESPOT'
Can you help me to learn more?
(Other definitions for despot that I've seen before include "Tyranical dictator" , "Gaddafi, say" , "Posted (anag)" , "Possibly 4 [CZAR]" , "Caesar for one" .)