Names That Mean Hollow

Cassio is a notable Shakespearean name that's a member of the ever-more-popular Cassius family of names.  Cassio was Othello's young, good-looking, and flirtatious lieutenant.

Cassio

A variation of Corey, this spelling has also been on a steady decline since the early-1990s. Its days are likely numbered on the US popularity charts altogether.

Cory

Anglicized spelling of a county in Ireland, sometimes considered a variation of the Breton Kavan or of Kevin.  Depending on your viewpoint, may make a fresh Kevin substitute or a choice that will drive you mad explaining that, no, it isn't Kevin.

Cavan

Perhaps if there's a Putnam in your background. 