cassandra
[noun]
Synonyms: pessimist, calamity howler, crepehanger, worrywart

[TahlilGaran] English Synonym Dictionary ▲

Cas‧san‧dra /kəˈsændrə/
people are sometimes called a ‘Cassandra’ if they warn that something bad will happen, but nobody believes them. In ancient Greek stories, Cassandra was the daughter of Priam, King of Troy. She had the power to see the future, and warned that the Greeks could use the Trojan Horse to take control of Troy, but no one believed her.

[TahlilGaran] Dictionary of Contemporary English ▲