What does "sibylline" mean?

Sibylline: Pertaining to the sibyls; uttered, written, or composed by sibyls; like the productions of sibyls. Sibylline books. (a) (Rom. Antiq.) Books or documents of prophecies in verse concerning the fate of the Roman empire, said to have been purchased by Tarquin the Proud from a sibyl. (b) Certain Jewish and early Christian writings purporting to have been prophetic and of sibylline origin. They date from 100 b. c. to a. d. 500.