Thickheaded spouse?, 7 letters
Blockhead, 6 letters
Chowderhead, 6 letters
Chucklehead, 6 letters
Doofus, 6 letters
Dumbbell, 6 letters
Idiot, 6 letters
Lamebrain, 6 letters
Nincompoop, 6 letters
No Einstein, this one, 6 letters
Not the brightest bulb on the Christmas tree, 6 letters
Not-too-bright sort, 6 letters
Numskull, 6 letters
(informal) a stupid incompetent person, 6 letters
Dunces, 7 letters
Knuckleheads, 7 letters
Noodleheads, 7 letters
Numskulls, 7 letters
Not-so-great plan, 15 letters