Blockhead, for short, 6 letters
Ass, 10 letters
Doofus, 10 letters
Fool, 10 letters
Knucklehead, 10 letters
Saphead, 10 letters
Silly goose, 10 letters
Simpleton, 10 letters
A stupid foolish person, 10 letters
Where to find a nitwit on a ship?, 14 letters
Boobs, 11 letters