Ash (5)
I believe the answer is:
ember
'ash' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for ember that I've seen before include "Glowing coal; type of goose" , "Glowing coal; prayer (Days)" , "Small piece of glowing coal in a dying fire" , "Hot piece of wood or coal from a fire" , "what causes a warm glow" .)