Interesting, in the US a blunt is a cigar or cigarillo emptied out and filled with weed, a joint is just a rolled cannabis cigarette, and a mix of tobacco and cannabis is a spliff.
When I was introduced to the term Spliff (which is fairly interchangeable) it was from dud3bros coming back from college trips to Europe. They would roll weed and tobacco and be all 'this is how they do it in Europe '. No shit weeds harder to get in europe! stop trying to burn my cali green with your wack ass tobacco !! (blunts are named after the type of Cigar you'd cut open. Philly Blunts)