Cause to burn (6)
I believe the answer is:
ignite
'cause to burn' is the definition.
(igniting is a kind of causing to burn)
This is all the clue.
(Other definitions for ignite that I've seen before include "Catch fire; provoke" , "Set fire to, light up" , "Kindle Fire" , "Put a match to" , "'Set alight, fire up (6)'" .)