The quality or state of being goofy; silliness, foolishness, or the tendency to act in a ridiculous or eccentric manner.
From 'goofy' plus the noun-forming suffix '-ness' (which creates abstract nouns from adjectives). This follows the same pattern as 'happiness,' 'sadness,' and thousands of other English abstract nouns.
English speakers love turning adjectives into abstract qualities with '-ness'—it's such a reliable pattern that we can create words on the fly and everyone understands them instantly, which is why 'goofiness' feels like it's always been a word!
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