Revolutionary communist, idiot that could ignite something (6)
I believe the answer is:
tinder
'that could ignite something' is the definition.
(tinder is used to start a fire)
'revolutionary communist idiot' is the wordplay.
'revolutionary' says the letters should be written backwards.
'communist' becomes 'red' (red is a kind of communist).
'idiot' becomes 'nit' (I've seen this before).
'red'+'nit'='rednit'
'rednit' in reverse letter order is 'TINDER'.
(Other definitions for tinder that I've seen before include "Touchwood" , "Dry stuff to help start fire" , "Dry stuff for starting fire" , "Firestarter" , "Dry stuff for lighting fire" .)