Manna, according to the Bible, 9 letters
Butterfingers, 6 letters
Clumsy clod, 6 letters
Dork, 6 letters
Foolish sort, 6 letters
Goofball, 6 letters
Idiot, 6 letters
Knucklehead, 6 letters
Pinhead, 6 letters
(informal) a stupid incompetent person, 6 letters
Nitwits, 8 letters