-thon

-thon

suffix forming nouns
indicating a large-scale event or operation of a specified kind: telethon.
[C20: on the pattern of marathon]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

-athon

or -a-thon,

a combining form extracted from marathon, having the general sense “an event, as a sale or contest, drawn out to unusual length, often until a prearranged goal is reached”: walkathon; readathon; bikeathon; workathon. Compare -thon.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.