The quality or state of being a chowderhead; stupidity or foolishness.
From chowderheaded plus the -ness suffix, creating a noun that abstracts the quality of stupidity. The nested suffixes (-ed then -ness) are characteristic of English word-building.
Chowderheadedness is the ultimate regional insult transformed into philosophy—it's New England slang elevated to an abstract noun, suggesting stupidity so complete and fundamental it deserves its own fancy word!
Complete word intelligence in one call. Free tier — 50 lookups/day.