vest versus waistcoat?

[Sir William]

I have always refered to a vest as I would a waistcoat.. but of course there are exceptions to everything...

I tend to use the two terms interchangeably as well, with the exception that I use waistcoat, or wesket, to refer to my 18th century garments.

I'm slightly curious as to when Americans began to refer to waistcoats as vests.