The quality or state of being elegant, stylish, and of high quality; sophistication and refined taste.
From 'classy' (elegant, high-class) plus the noun-forming suffix '-ness.' Emerged in informal English in the mid-20th century.
It's amusing that 'classiness' came from American slang to describe something sophisticated—the opposite of what 'class' meant socially, yet it captured something true about elegance being visible to anyone.
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