a for·ti·o·ri (ä fôr?t?-ôr??, ?)adv. For a still stronger reason; all the more.[Latin ? forti?r? : ?, from + forti?r?, ablative of fortior, stronger.]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.a fortiori (e? ?f??t????ra?; -r?; ??) advfor similar but more convincing reasons: if Britain cannot afford a space programme, then, a fortiori, neither can India. [Latin]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014a for?ti?o?ri (? ?fo?r t??o? ri; Eng. e? ?f?r ?i??r a?, e? ?fo?r ?i?o?r a?) adv. Latin. for a still stronger reason; even more certain; all the more. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.a fortioriA Latin phrase meaning for a stronger reason.Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited