-ialsuff. Of, relating to, or characterized by: baronial.[Middle English, from Old French, from Latin -i?lis.]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.-ial suffix forming adjectives of; relating to; connected with: managerial. [from Latin -i?lis, adj suffix; compare -al1]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014al- var. of ad- before l: allure. -al1 , a suffix with the general sense ?of the kind of, pertaining to, having the form or character of? that named by the stem, occurring in loanwords from Latin (autumnal; natural; pastoral), and productive in English on the Latin model, usu. with bases of Latin origin (accidental; seasonal; tribal). Compare -ical, -ar 1, -ial. [