I was reading a question here about the use of the suffix -gate to denote a political, and later any type, of scandal. This is of course and allusion to the Watergate scandal, which lead to the resignation of President Nixon.
Another example came to mind, that of Marathon, which is the name of a long race, and is named after the battle of Marathon, and more specifically Pheidippides run back to Athens to announce victory (and then die, this secondary aspect being thankfully absent in the Olympic event.) From this the -thon suffix is used to denote any long endurance event, phone-athon, bake-athon, jump-athon etc.
I was wondering if there were any other such false back formations that have come into common use in the same way. Is there a specific name for this practice in grammar?