Definitions of dunderhead on the Web:

dunce: these words are used to express a low opinion of someone's intelligence

wordnet.princeton.edu/perl/webwn

The Dictionary of Americanisms offers: "DUNDERHEAD. Blockhead; dolt. The same as the English provincialisms dunder-knoll and dummer-head."

The American Heritage concurs in the possibility of the term deriving from doner, thunder, in Middle Dutch.


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