Left to set fire to coal (7)
I believe the answer is:
lignite
'coal' is the definition.
(lignite is a kind of coal)
'left to set fire' is the wordplay.
'left' becomes 'l' (common abbreviation).
'to set fire' becomes 'ignite'.
'l'+'ignite'='LIGNITE'
'to' is the link.
(Other definitions for lignite that I've seen before include "it'll burn" , "Soft brownish coal" , "rock" , "Fuel" , "Brown coal" .)