The quality or state of being cheery; brightness, happiness, and optimism.
From 'cheery' plus the noun-forming suffix '-ness,' which creates abstract nouns describing qualities. The '-ness' suffix is one of the most productive in English, allowing adjectives to become nouns.
The '-ness' suffix is so useful that English speakers unconsciously create new nouns with it—you might hear 'the silliness of that joke' or 'the randomness of it all,' and these new combinations are instantly understood because the pattern is so familiar.
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