idiot (n.)
An idiot is a fool. The word comes from the Greek idiōtēs, from idios, one’s own, private. An idiōtēs was a private person: not in the public eye, holding no office.12
It said nothing about intelligence. It described what a person did not take part in. From there the word went to the common man, and from the common man to the ignorant one, since ordinary people were not generally the ones with the learning.12
English took it in that ignorant sense and then narrowed it again, from a man without education to a man without sense.2
Some idiot had left the gate open.