In Russian, идиот has two uses in the book that intersect. One is diagnostic: Dr. Schneider treats idiocy and madness in a sanatorium in the Valais, and the prince himself says that his fits made him, as a child, almost an idiot. The other is an insult: Ganya calls him a damned idiot, Aglaya murmurs it at the vauxhall, and the prince, after offering money to Burdovsky in public, calls himself a true idiot.
Where It Appears
Quotes
everyone also takes me for an idiot, I don't know why; in fact, I was once so ill that at that time I did seem like an idiot; but what kind of idiot am I now, if I myself understand that they take me for one? I go in and think: here they take me for an idiot, and yet I am intelligent, and they don't suspect a thing...
Part One: The Arrival, Myshkin
And if Schneider himself came now from Switzerland to see his former pupil and patient, he too, remembering the state the prince sometimes fell into during the first year of treatment in Switzerland, would now make a gesture of dismay and say, as he did back then: "Idiot!"