Like many other English terms, the term ‘moron’ is a loan word from Greek. The term ‘moron’ is derived from the Ancient Greek ‘moros’ which means “dull”. The modern definition of the word has not changed. Moron, today, is used to refer to someone who is considered stupid or dim-witted, i.e. ‘dull’-minded.
The term ‘moron’ was once used as a psychological term, in addition to others, such as “idiotic”, “imbecilic”, “stupid”, and “feeble-minded”. As a psychological term it was used for someone with an IQ between 51 and 70, while 90 to 109 is considered as average.
However, the term gained popularity as an informal term, similar to idiot or stupid, and was discontinued as a psychological term around the dame time.