Source : Webster's Revised Unabridged Dictionary (1913)

Sibylline \Sib"yl*line\, a. [L. sibyllinus.]
   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.

Source : WordNet®

sibylline
     adj 1: resembling or characteristic of a prophet or prophecy; "the
            high priest's divinatory pronouncement"; "mantic
            powers"; "a kind of sibylline book with ready and
            infallible answers to questions" [syn: {divinatory}, {mantic},
             {sibyllic}, {vatic}, {vatical}]
     2: having a secret or hidden meaning; "cabalistic symbols
        engraved in stone"; "cryptic writings"; "thoroughly
        sibylline in most of his pronouncements"- John Gunther
        [syn: {cabalistic}, {kabbalistic}, {qabalistic}, {cryptic},
         {cryptical}]