When something has showiness, it means it is very bright, colorful, and attention-grabbing.
Showiness can be good if you want to be noticed, but it can also be too much and not very tasteful.
Examples:
Her dress has a lot of showiness with all those sparkles.
The showiness of the fireworks amazed the children.
The showiness of the peacock's feathers caught everyone's eye.
The showiness of his outfit made everyone laugh.
The showiness of the decorations was so bright it hurt my eyes.
The showiness of the parade made it the best one ever.