-thon

-thon

suffix forming nouns
indicating a large-scale event or operation of a specified kind: telethon.
[C20: on the pattern of marathon]

-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.