The name Sibyl is a girl's name of Greek origin meaning "seer, oracle". Sibyl and is often added to lists like Greek Baby Names for Modern Kids and discussed in our forums with posts like "Quintuplets (girls)".
From the experts:
The original but less common spelling of the ancient mythological name, now used mostly for fictional witches. But the rise of the lovely Lady Sybil Crawley on television's Downton Abbey and the fall of the multiple personality Sybil, a self-confessed fake, may give Sibyl and Sybil more credibility as a name.