The Middle French word 'toile' ("cloth") had a diminutive form: 'toilette', or "small piece of cloth." This word became 'toilet' in English, and referred to a cloth put over the shoulders while dressing the hair or shaving.
oh I finally get what you're saying. You're taking issue with calling that room "rest" room instead of "toilet"
but seeing as "toilet" literally means "a small piece of cloth" - if we're going to go down that path, why are you calling both the room and it's commode a piece of cloth?
Oooooh it's just Americans with their funny words for things.
Obviously they mean lavatory, toilet, loo, shitter, bog, water closet, facilities, tile palace, WC, khazi, ceramic throne of dreams, privy, latrine, etc.
There are many reasons toilets are called the restroom dated back in history. However these days it's mostly just considered a polite way of taking care of one's business, without projecting to a partner that you may be taking a massive duce.