-athonsuff. An activity that continues for an extended period of time: phonathon; talkathon.[From (mar)athon.]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.-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.