Glowing piece in a dying fire (5)
I believe the answer is:
ember
'glowing piece in a dying fire' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ember that I've seen before include "Glowing coal; type of goose" , "Glowing, smouldering piece of coal or wood" , "Just a glimmer" , "It glows in dying fire" , "what causes a warm glow" .)