Shininess is how smooth and bright something looks — how much light comes back at you from its surface. A polished table, a new coin, wet hair, or a clean window can have a lot of shininess. We use it for things you can see, not for a person’s character. It is a quiet, slightly school-like noun; in everyday talk people more often just say “how shiny it is.” You might meet it in science when you compare metals, or in a shop when someone talks about the shininess of a floor or a car.

光澤、閃亮的程度