Residue of fire (3)
I believe the answer is:
ash
'residue of fire' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ash that I've seen before include "Tree in danger" , "Hardwood" , "blonde" , ". . . . [FOREST] One of which" , "Powdery residue from fire or cigarette" .)