Can I call a window sill window stool?
This article, which is just one among the very many I found on the internet, says that what is commonly referred to as the "sill" is actually the stool, the sill being outside of the home and the stool inside.
Personally, when I found myself in this kind of situation, I generally tend to prefer the "proper" option, that is "stool" in this case.
But upon running a search on ngram I found out that the word "stool" is not simply less used; it's virtually non-existent. So I was wondering whether this time I might be better off choosing "sill", for the sake of clarity.