The quality or state of being brunette; having dark brown hair, especially as a physical characteristic or appearance.
From brunette (French, feminine form of brunet meaning 'dark brown,' from brun meaning 'brown') plus -ness suffix indicating a quality or state.
Adding -ness to adjectives to make abstract nouns is one of English's most productive patterns (darkness, kindness, wetness), and brunetteness is a humorous formal example of turning a hair color into a philosophical quality.
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