sibylline : Idioms & Phrases

• . (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.

Webster 1913