a suffix extracted from marathon, occurring as the final element in compounds which have the general sense “an event, as a sale or contest, drawn out to unusual length, often until a prearranged goal, as the contribution of a certain amount of money, is reached”: walkathon; readathon.
Also -a-thon, -thon.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
also -thon, word-forming element denoting prolonged activity and usually some measure of endurance, abstracted from marathon. E.g. walkathon (1931), skatathon (1933); talkathon (1948); telethon (1949).
Online Etymology Dictionary, © 2010 Douglas Harper