We have all been called a moron at one time or another and understood it to mean we’ve done something foolish.
The reason is that in 1910 Dr. Henry H. Goddard (1866-1957) proposed the word to the American Association for the Study of the Feeble minded to describe an adult with the mental capacity (IQ below 75) of a normal child between eight and twelve years of age.
A moron was, in fact, the highest proposed rating of a mentally challenged person.
The two lowest ratings suggested were imbecile and idiot.
These categories have been dropped by the scientific community and are no longer in use, except as an insult.
The word moron is from the Greek moros, meaning “stupid” or “foolish.”