regnal definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
of a sovereign, sovereignty, or reign
Origin: Midieval Latin regnalis ; from Classical Latin regnum, reign
regnal definition by American Heritage Dictionary
Being a specified year of a monarch's reign calculated from the date of accession: in her 12th regnal year.
Origin: Medieval Latin rēgnālis, royal, from Latin rēgnum, reign; see reign.