The Collaborative International Dictionary of English v.0.48:

Sibylline \Sib"yl*line\, a. [L. sibyllinus.]
   Pertaining to the sibyls; uttered, written, or composed by
   sibyls; like the productions of sibyls.
   [1913 Webster]

   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.
       [1913 Webster]