Imbecile (5)
(Other definitions for moron that I've seen before include "Fool" , "Complete imbecile" , "Cretin" , "Somewhat feeble-minded person" , "Clot" .)
'imbecile' is the definition.
(I know that imbecile can be written as idiot)
This is all the clue.
(Other definitions for idiot that I've seen before include "Dostoevsky hero" , "Charlie" , "one needing head examined?" , "Stupid person" , "Dope" .)