What do you call it?

Okay, here's my question, or questions. Not particularly important, but I'm curious.

Why is the restroom called the restroom? We don't exactly rest in there.

And why is it that we say, "I need to go to the bathroom," when we don't plan to take a bath but only to use the toilet?

When I was in elementary school, the place was called The Lavatory. Yes, we did wash our hands in there, or we were supposed to . . . after we used the toilet, which is why we went in there.

Outhouse I see. I mean it is outside of the house. But still it avoids the word "toilet."

It isn't a bad word, toilet, and has been used historically to mean something other than the way we use it today, as in A Lady at her Toilet, which was where she put the final touches on her hair and makeup. Or her personal maid did those things for her. The Lady could be sitting or standing, and it was usually done in her bedroom, facing a mirror, not in the "bathroom."

But that information I insert only so you will know I know about it. Really, it may have little to do with my original question, but it does raise another question.

How did that use of the word "toilet" change to the toilet we know?