Definition of "dinderhead"

Lawks, doant be clummed by Babbin Enapp, 'Sa bibbling, boostering, brinded chap, A dinderhead hadge-boar!

1867, William Frederick Rock, Jim and Nell: A Dramatic Poem in the Dialect of North Devon. By a Devonshire Man‎

Being only a dim gentile I could not see the slightest connection between fish and guns, until, by now getting quite angry at my stupidity she roared in my ear "game-kipper (keeper), game-kipper, y'er dinderhead."

1971, Journal of the Gypsy Lore Society‎, The Society