The Collaborative International Dictionary of English v.0.48:

Numskull \Num"skull`\, n. [Numb + skull.]
   A dunce; a dolt; a stupid fellow. [Also spelled numbskull.]
   [Colloq.]
   [1913 Webster]

         They have talked like numskulls.         --Arbuthnot.
   [1913 Webster]