In English, name Cassie means – Unheeded prophetess. A diminutive of Casirnir, Cassandra, or Catherine. Cassandra was a Trojan prophetess, daughter of King Priam. In Homers The Iliad Cassandras prediction of the fall of Troy was unheeded. Also used as an independent name.. Other origins for name Cassie include – English, Greek. Name Cassie is most often used as a girl name or female name.