Powdery residue (3)
I believe the answer is:
ash
'powdery residue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ash that I've seen before include "Fire's remains" , "What's often left after something 1 Ac" , "Wooden" , "End of fire" , "at village near Whitchurch in Shropshire" .)