In 1982, William Safire called that “one of the great etymological mysteries of our time.” He himself thought that the phrase originally referred to the capacity of a cement truck in cubic yards. But there are plenty of other theories. Some people say it dates back to when square-riggers had three masts, each with three yards supporting the sails, so the whole nine yards meant the sails were fully set. Another popular story holds that it refers to the length of an ammunition belt on World War II fighters — when a pilot had exhausted his ammunition he said he had shot off the whole nine yards. Or it was the amount of cloth in the Queen’s bridal train or the Shroud of Turin. Or it had to do with a fourth-down play in football. Or it came from a joke about a prodigiously well-endowed Scotsman who gets his kilt caught in a door.