The quality or state of being dotty; scatterbrained or eccentric behavior.
From 'dotty' with the noun-forming suffix '-ness', which is one of the most common ways English creates abstract nouns from adjectives.
The suffix '-ness' is incredibly ancient—it comes from Old English and Norse roots—and allows us to talk about qualities as if they're things we can measure, which is a clever cognitive trick English uses constantly.
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