Come and learn new word... not bad...
imbecile =
Noun:
1. A stupid or silly person; a dolt.
2. A person whose mental acumen is well below par.
3. A person of moderate to severe mental retardation having a mental age of from three to seven years and generally being capable of some degree of communication and performance of simple tasks under supervision.
Adjective:
1. Stupid; silly.
2. Well below par in mental acumen.