Doom celebration, we hear (4)
I believe the answer is:
fate
'doom' is the definition.
(I've seen this before)
'celebration we hear' is the wordplay.
'celebration' becomes 'fete' (fete is a kind of celebration).
'we hear' indicates a 'sounds like' (homophone) clue.
'fete' sounds like 'FATE'.
(Other definitions for fate that I've seen before include "Destiny, kismet" , "One's lot" , "Predetermined end" , "Lot -- doom" , "What must be" .)