Coal's left out to light (6)
I believe the answer is:
ignite
'light' is the definition.
(thesaurus)
'coal's left out' is the wordplay.
'coal' becomes 'lignite' (lignite is a kind of coal).
'left' becomes 'l' (common abbreviation).
'out' suggests deleting specific letters.
'lignite' with 'l' removed is 'IGNITE'.
'to' acts as a link.
(Other definitions for ignite that I've seen before include "Kindle Fire" , "Touch off; inflame" , "Cause to start burning" , "Put a match to" , "Torch" .)