regnal
reg·nal
(rĕg′nəl)adj.
Being a specified year of a monarch's reign calculated from the date of accession: in her 12th regnal year.
[Medieval Latin rēgnālis, royal, from Latin rēgnum, reign; see reign.]
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.
regnal
(ˈrɛɡnəl)adj
1. (Government, Politics & Diplomacy) of a sovereign, reign, or kingdom
2. (Government, Politics & Diplomacy) designating a year of a sovereign's reign calculated from the date of his or her accession
[C17: from Medieval Latin rēgnālis, from Latin rēgnum sovereignty; see reign]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
reg•nal
(ˈrɛg nl)adj.
of or pertaining to a sovereign, sovereignty, or reign: the second regnal year of Louis XIV.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.