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1. A title of no legal validity that is assumed or granted by custom, such as the academic title professor given to any instructor at a college.
a. In Great Britain, the title that the heir of a high-ranking peer customarily uses, consisting of a secondary title accorded to the peer.
b. In Great Britain, the prefixes Lord and Lady added to the given names of the younger children of dukes and marquises or the Honourable added to the children of viscounts and barons.
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.
(Government, Politics & Diplomacy) any of several titles having no legal significance, such as those borne by the children of peers
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
a title allowed by custom, as to the children of dukes.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.