'moron' originates from Greek, specifically the word 'moros', where 'moros' meant 'dull, foolish'.

'moron' was adopted into English in the early 20th century (used in psychology and psychiatry as a clinical term) from Greek 'moros' (via Modern Latin/Medical use), and later shifted into general slang/insult.

Initially, it meant 'a person with mild intellectual disability' in a clinical sense, but over time it evolved into its current meaning of 'a stupid or foolish person' and became an insulting colloquial term.