Moron

A mentally retarded person whose intellectual development proceeds normally up to about the eighth year of age and is then arrested so that there is little or no further development; an adult having the mental development of an 8-to-12-year old. A moron is considered capable of doing routine work under supervision.(Pedagogy)

Hence, a very stupid person.[informal, derogatory]

An inferior olive size having a woody pulp and a large clingstone pit, growing in the mountainous and high-valley districts around the city of Moron, in Spain.