It dies eventually at the end of four months (5)
I believe the answer is:
ember
'it dies' is the definition.
(the embers are the dying remains of a fire)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ember that I've seen before include "Smouldering piece of dying fire" , "Material in dying fire" , "Fire remnant" , "Piece of live coal" , "Hot piece of wood or coal from a fire" .)