The Collaborative International Dictionary of English v.0.48:

Muddlehead \Mud"dle*head`\, n.
   A stupid person; a blunderer. [Colloq.] --C. Reade. --
   Mud"dle-head`ed, a. [Colloq.] --Dickens.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "muddlehead":
   addlebrain, addlehead, addlepate, beefhead, blockhead, blubberhead,
   blunderhead, bonehead, bufflehead, cabbagehead, chowderhead,
   chucklehead, clodhead, clodpate, clodpoll, dimwit, dolt, dolthead,
   dullhead, dumbbell, dumbhead, dunderhead, dunderpate, fathead,
   idiot, jolterhead, jughead, knucklehead, lunkhead, meathead, moron,
   mushhead, muttonhead, noodlehead, numskull, peabrain, pinbrain,
   pinhead, puddinghead, pumpkin head, puzzlehead, simpleton,
   stupidhead, thickhead, thickskull, tottyhead