Sorry, Les, I don't think it is rare. A word played by roughly 62.5% of those taking part in a game must be classed as 'common'.
Over my years of playing Chi, I've come to accept that many words that I would regard as 'American'and probably never use myself : (rube, stogie, sass/sassy to quote just three examples) are probably 'familiar to native speakers everywhere in the English-speaking world' and consequently 'common' in the the world's favourite online word-game.
Put it down to the Internet, to pop songs, to Hollywood, To TV (Netflix is currently in the process of taking control of the televiewing habits of the entire world), to whatever, we have to (albeit reluctantly in some cases) accept that 'American' is now the dominant form of English.