Revolutionary spoke about Chennai leader (7)
I believe the answer is:
radical
'revolutionary' is the definition.
(synonyms)
'spoke about chennai leader' is the wordplay.
'spoke' becomes 'radial' (I've seen this before).
'about' means one lot of letters goes inside another.
'leader' says to take the initial letters.
The initial letter of 'chennai' is 'c'.
'radial' going around 'c' is 'RADICAL'.
(Other definitions for radical that I've seen before include "'Revolutionary, extremist (7)'" , "Progressive; extreme" , "Going to the root" , "Innovative, progressive" , "Thoroughgoing - (popularly) extremist" .)