You don't need me, Jack! You've got it exactly right. The only difference is in usage. In athletics, there is the 'triple jump' and no-one would ever call it the 'treble jump'. Similarly, no-one would go into a bookmaker's shop and place a bet on a 'triple' at Ascot. It's a bit like 'regal' and 'royal'...both come from 'king-like', the first from Latin and the second from French. By the same token, none of us would speak of 'the regal family' when speaking of the inhabitants of Buckingham Palace. Cheers