The quality or state of being cabbageheaded; stupidity or foolishness.
From 'cabbageheaded' plus the abstract noun suffix '-ness,' creating a noun meaning the condition of being stupid.
Creating 'cabbageheadedness' as an abstract noun is hilariously overkill—it's like taking a simple vegetable insult and turning it into a philosophical quality, which is very 18th-19th century!
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