There is so much to it! In Germany, where 'c' was replaced by 'k' only later, it started as 'Wasser Closet' , from 'water closet' - WC. For a German child, 'WC' had something mysterious to it. It wasn't just a 'toilet' - it was a WC! First time in Hawai'i, I was asking people for the WC - as it would work in Europe. Nobody knew what I was talking about. Until somebody told me "It's 'rest room'".
But I never met anybody in there that was resting.

I also found it always strange to call it a 'toilet bowl', where I use a bowl for different purposes...