whomso

whom·so

 (ho͞om′sō)
pron. Archaic
The objective case of whoso.
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.

whomso

(ˈhuːmsəʊ)
pron
whomwhomsoever
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

who•so

(ˈhu soʊ)

pron. objective whom•so.
whosoever; whoever.
[1125–75; Middle English, early Middle English hwa swa, Old English (swā) hwā swā. See who, so1]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.