Meaning and information about Cassie, What does Cassie mean? Cassie means Unheeded prophetess. A diminutive of Casirnir, Cassandra, or Catherine. Cassandra was a Trojan prophetess, daughter of King Priam. In Homer's 'The Iliad' Cassandra's prediction of the fall of Troy was unheeded. Also used as an independent name. Find similar names like Cassie.