The most shiny or glossy.
Sheeniest is a word used to talk about things that are very shiny or glossy, like a polished floor or a new car.
Examples:
The sheeniest car in the showroom caught everyone's eye.
Her sheeniest shoes sparkled in the sunlight.
The sheeniest marble floor reflected the light beautifully.
The sheeniest apple in the basket looked almost fake it was so shiny.
The sheeniest diamond in the world was worth a lot of money.
The sheeniest trophy was the biggest and best.