Sibyl

To the ancient Greeks and Romans, a sibyl was a woman who lived in a cave and uttered prophecies. Ten Sibyls were known by the places where they lived. For example, the Sibyl of Cumae lived in a cavern near Naples. My brother and his wife gave me a drawing of this cavern from when they lived near there.

English word: We still use the word sibyl to refer to a prophetess, and the adjective sibylline means "oracular."

Cassandra

In Greek myth, Cassandra was a princess of Troy. Apollo fell in love with her and gave her the gift of prophecy. She rejected his advances, so he changed the gift so that nobody would believe her, even though her prophecies came true.

English word: A Cassandra is a prophet/ess of evil who is not believed.