Judgment day; the day of divine reckoning when all souls face judgment, often capitalized as Doomsday when referring to an apocalyptic final day.
From Old English 'dōmes dæg' (day of judgment, literally 'day of doom'). 'Doom' comes from Old English 'dōm' (judgment), not from death necessarily.
The Domesday Book, William the Conqueror's 1086 census of England, was named as if it were final and inescapable—just like Judgment Day—because once you were written in it, your property was recorded for eternity.
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