in·ten·tion·al (?n-t?n?sh?-n?l)adj.1. Done deliberately; intended: an intentional slight. See Synonyms at voluntary.2. Having to do with intention.in·ten?tion·al·ly adv.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.