Taken from another forum but if enough people get involved it can be a cracker and can go on forever or be a big fail 
... but seriously it's great way to waste a few seconds of your day and be very interesting. 
..... so once the starting word has been chosen, the next player will find a word that they associate with it and make it known to everyone, the next player must then do the same with this word and repeat..... starting word:
Empty
