One of the Sibylline Oracles or Sibylline Books.
Having oracle-like predicting powers, clairvoyant.
Occult, mysterious.
Of or pertaining to or resembling a sibyl or female oracle, especially the Cumaean Sibyl and the Sibylline Books.
Excessively and exorbitantly expensive. (In allusion to the Sibyl who sold three books to Tarquinius Superbus at the price of the original nine.)