Reportedly celebrate doom (4)
I believe the answer is:
fate
'doom' is the definition.
(I know that doom can be written as fate)
'reportedly celebrate' is the wordplay.
'reportedly' shows a homophone (sound like).
'celebrate' becomes 'fete' (synonyms).
'fete' sounds like 'FATE'.
(Other definitions for fate that I've seen before include "Clotho, Lachesis or Atropos" , "E.g. Clotho, Atropos" , "Destiny, kismet" , "Inevitable destiny" , "Final issue" .)