Casey /ca-sey/ [2 sylls.] as a girls' name (also used more regularly as boys' name Casey) is pronounced KAY-see. It is of Irish and Gaelic origin, and the meaning of Casey is alert, watchful. From the male Gaelic name Cathasaigh.Also variant of Cassie and diminutive of Acacia.Made famous by the popular song about the heroism of Luther Casey Jones, a US engine driver who died to save the lives of his passengers.asey is a very prominent first name for females (#461 out of 4276, Top 11%) and also a very prominent last name for both adults and children (#463 out of 150436, Top 1%). (2000 U.S. Census). Displayed below is the birth name popularity of Casey for girls.