The quality or state of being a chucklehead; stupidity, foolishness, or silliness.
From 'chuckleheaded' (foolish) plus '-ness' suffix, creating an abstract noun that describes the quality of foolishness itself.
This word is a perfect example of how English can stack suffixes—'chuckle' + 'head' + 'ed' + 'ness'—creating impressively long words from simple roots, though most people would just say 'stupidity'!
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