It dies eventually at the end of four months (5)

I believe the answer is:

ember

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'it dies' is the definition.
(the embers are the dying remains of a fire)

I can't explain the remainder of the clue.

(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" .)

I've seen this clue in The Globe and Mail.

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