The words idiom and idiot differ only in the final letters: t and m. So I was wondering - do these words have a common root? If so, how have the t and m changed this root?
This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information. See the FAQ for guidance on how to improve it.
I suspect this may be general reference, but from the OED:
Etymology of idiot:
Etymology of idiom:
So it appears that they share a very distant root (idio-) but their meanings would have been distinct even in ancient Greece by virtue of the endings.