'simpleton' originates from the word 'simple,' combined with the suffix '-ton,' which was used to form nouns indicating a person characterized by a certain quality.

'simple' transformed into 'simpleton' in the late 17th century, indicating a person of simple or foolish nature.

Initially, it meant 'a person of simple nature,' but over time it evolved into its current meaning of 'a foolish or gullible person.'