Is·ma·i·li (?s?mä-??l?) also Is·ma·i·li·an (-??l?-?n)n. pl. Is·ma·i·lis also Is·ma·i·li·ans A member of a branch of Shiism that follows a living imam and is noted for esoteric philosophy.[Arabic Isma’?l?y, after Isma’?l (died 760), son of the sixth imam, Jafar (700?-765).]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.