Cassie is a diminutive of Cassandra. Cassandra originates in Greek language and means "shine upon mankind". In Greek mythology, Cassandra, King Priam's daughter, was a prophet. Apollo cast a curse on her so that nobody would ever believe her prophecies. Eventually, the gift of prediction resulted in endless frustration. Cassandra has been an inspiration for many artists and authors. In the U.S. the name became popular in the 20th century.