A periwinkle is a tiny snail that lives in the Atlantic Ocean. Some east coast beaches are covered with small stones, shells, and periwinkles. It’s also a color, a purplish-blue, just like the flowers on a periwinkle plant.
You might see periwinkles as you walk along the sea shore, and you may even see them on some restaurant menus, especially in coastal areas of the UK, where they're commonly called winkles. Another kind of periwinkle is the blue-flowered plant also called vinca, as well as the shade of purplish blue that was named for the flowers. Periwinkle is fun to say.