According to the Oracle, SIBYLS is the plural of Sibyl. There weren’t many of them, but they were a singular lot.
SIBYLS were fortune tellers. Girls who chewed laurel leaves and other funny substances, spouting strange gibberish which was alleged to be the words of the Gods. They started off in the Greek world but were still going strong in Roman times. See, for example, ALBUNEA, SIBYL-OF-CUMAE(2).
For a small consideration plus service charge, priests would translate these into prophecies. Much more fun than Horoscopes and extremely popular.