I was listening to BBC World on NPR the other day and was surprised to hear the reporter use the term “fortnight”. That would never happen in the US, as that term is considered archaic. I doubt that even 50% of the population would understand what it meant.
So, is that common usage in Britain?
How about “score”? Most Americans would recognize “Four score and seven years ago”, but I’m not sure many would actually know that it means 87 years ago.