A person who believes or declares that something is already destined to fail or end badly.
From 'foredoom' + '-er' (agent suffix). This creates a noun meaning one who foredooms, following English word-formation patterns dating back to Old English.
Cassandra from Greek mythology would be history's most famous 'foredoomer'—she could see the future and always predicted doom, but nobody believed her, making her the ultimate tragedy.
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