We get the word idiot directly from French idiote, from Latin idiota. The former word meant "dumb person", but the latter meant more along the lines of "uneducated person", which makes all the difference as we go further back to Greek idiotes, or "commoner" (a case where, as we've seen before, the highborns who could read created derogatory words for the lower classes). Since the Greeks had democracy and considered the commoners private citizens, the connection existed for the term to trace to the earlier idios, meaning "private", probably from Proto-Indo-European swe, defined as "self". Now, the word idios also gave way to another Greek word, idioumani, which had the complicated meaning of "something that is privately peculiar". As this became Greek idioma, it meant something more like "peculiar", but still described things that are unique to small groups. This definition stayed through Latin idioma, French idiome, and finally English idiom. So it may be idiotic, but two words in this idiom are peas in a pod.
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