Half of British homes have a Scrabble set; 150 million have been sold around the world since the game took off in the 1950s. Barack Obama loves it. So did Vladimir Nabokov. But informal playing with family and friends is only part of the picture. There is also competitive, international Scrabble.

If you want to play Scrabble at championship level, you need to memorise lists of words, particularly two-letter words, and you need to know which words are allowed. The US and Canada use the Official Scrabble Players Dictionary (OSPD), which contains all allowable words up to eight letters, plus inflections of shorter words. It does not include offensive words, although they are allowed in tournaments. There is a special tournament Word List. I like to think it comes in a glass box with a hammer, “for use only in emergency”.

Elsewhere in the English-speaking world we use the Collins Official Scrabble Words list (known as CSW). It includes many more words than OSPD, because we allow US spellings as well as ours and because it includes words up to 15 letters. It’s not a dictionary. As it only lists the words, it is not very exciting. Unless, that is, you are a serious Scrabble player, in which case CSW is of burning interest. Every four years, the book is updated.