The Simple English Wiktionary has a definition for: idiot.

Idiot is a word used to describe someone who is not very smart.

Today "idiot" is often used to show that someone has done something which was not very clever:

• "You idiot, look at what you just did!" (using the word as a noun)
• "I think that idea is perfectly idiotic." (using the word as an adjective)

The word "fool" is similar to "idiot", but it is not as strong. In the history of drama a "fool" was a jester: someone who made people laugh. Kings often had jesters in real life. A court jester had the job of making the king feel happy when he was sad. Jesters often pretended to be stupid, but were actually very clever. There are jesters and fools in a lot of Shakespeare’s plays.

The word simple can also be similar to "idiot". Someone who is simple is a person who is not very clever or "streetwise". They are naïve and can easily be made to believe things because they are kind and expect everyone else to be kind as well. Such people are often called simpletons.

Idiots or simpletons are commonly used in literature. In German literature (and in Wagner’s opera), Parsifal is described as "perfect fool" because he does not understand the evil ways of the world and is therefore completely good. That is why he can break the magic spell cast by Klingsor. The idiot often appears in Russian literature. Because the idiot is so simple he (it is always a male) is often able to express the truth which other people cannot see. Dostoevsky wrote a novel called The Idiot. It is about a man who is simple and trusting. At the end of the opera Boris Godunov by Mussorgsky the crowd of poor people gather round the simpleton who is the last person to sing in the whole opera. His moans express the fact that Russia will continue to be ruled by cruel dictators and the people will remain poor.

The word "idiot" refers to a genetically incompetent human who is mentally inert on exposure to others - may have dampened senses and mental acuity when applied to any relatively simple task from long periods spent in a dark cave: the idiot's "natural habitat". Idiots tend to be ignorant of any metal and physical deficiency within themselves, simply because they do not want to believe it exists (even though it does, and they are aware of it). Mental deficiencies of others however, are overtly proclaimed by the idiots in order for them to separate themselves from habitual human tendencies, though they succumb to them more than they intend. They make no effort to rectify these though, as they view themselves in the best possible light.