The quality of being chubby; plumpness or roundness of the body.
From 'chubby' plus the noun-forming suffix '-ness,' a productive suffix in English that creates abstract nouns from adjectives describing qualities.
The '-ness' suffix is so powerful in English that you can add it to almost any adjective to create a noun, which is why speakers invented countless words like 'chubbiness' to talk about qualities without needing totally different root words!
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