The quality or state of being glossy; shininess, smoothness, or a superficially attractive appearance.
From 'glossy' + '-ness' (suffix creating abstract nouns). The noun form allows us to discuss the abstract quality of being shiny or polished.
The glossiness of a finish can be measured scientifically with a 'gloss meter' at precise angles—a surface with 100% gloss reflectivity at 60 degrees is considered perfectly mirror-like!
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