sib·yl·line (s?b??-l?n?, -l?n?) also si·byl·ic or si·byl·lic (s?-b?l??k)adj.1. Coming from, characteristic of, or relating to a sibyl.2. Prophetic; oracular.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.