"Billion" means a thousand million. Incredibly, it wasn't too long ago that the British used "thousand million" for "billion," and used "billion" for our "trillion." They eventually awoke to the folly of their ways, and adopted what is called the short scale. People don't even understand these quantities when they are consistent, and having two confusing systems for them might possibly lead to millions, or billions, or even trillions of mental breakdowns worldwide.
Until the recent adoption of the euro in Italy, the word "millionaire" was translated by the word miliardario, due to the strong inflation of the lira. It is now back to milionario, as it was in Italy many decades ago.