Find an word which is singular, add an 's' and it becomes plural, and add another 's' it becomes singular again?
Share link: www.brainbashers.com
One of answers involves royalty.
Prince, princes, princess.
Bra, bras, brass.
A similar change is care, cares, caress, but these are not nouns.
Note: BrainBashers has a Dark Mode setting.