jack [LME] In the Middle Ages Jack, a pet form of John, was used to refer to any ordinary man, much as Tom, Dick, and Harry is today. By the 16th century it also meant a young man, and from this we get an alternative name for the knave (from the Old English for ‘boy’) in cards. In the 18th century a jack was a labourer, which gives us the second part of words like lumberjack [M19th] and steeplejack [L19th], a sense extended to various mechanical devices. A jack was also an unskilled worker as contrasted with the master of a trade who had completed an apprenticeship, from which we get the saying jack of all trades and master of none [E17th]. On the other hand, the apprentice could assert his equality with the words Jack is as good as his master [L18th]. See also jockey.

A jack can also be a thing of smaller than normal size. Examples include the jack in bowls [E17th]—a smaller bowl placed as a mark for the players to aim at—and jack as in Union Jack [L17th], which is strictly speaking a small version of the national flag flown on board ship. Jack-o-lantern [M17th] as a name for a pumpkin lantern made at Halloween looks back to an earlier use of the phrase. In the 17th century it was a name for a will-o’-the-wisp [E17th], a light seen hovering at night over marshy ground, from another common first name—exchanging the idea of Jack with a lantern for Will with a ‘wisp’, or handful of lighted hay. I’m all right, Jack is an early 20th-century catchphrase used to express selfish complacency, which became the title of a film starring Peter Sellers in 1959. The Jack Russell terrier is named after a 19th-century English clergyman, known as ‘the Sporting Parson’, who was famed in hunting circles for breeding these terriers. Today a jackpot [M19th] is a large cash prize in a game or lottery. The term was originally used in a form of poker, where the pool or pot accumulated until a player could open the bidding with two jacks or better.