/dʒæk/
[noun] A common name used to refer to an ordinary man or a general helper, and also a device used for lifting heavy objects such as cars.
Jack was once so common a name for the average Englishman that it became a word for any man — and then for any machine that did a man's work.
The story of 'jack' begins with a name. In medieval England, 'Jack' was a nickname for 'John', which itself came from the Old French 'Jehan' and before that from the Latin 'Johannes', rooted in the Hebrew 'Yohanan', meaning 'God is gracious'. John was so breathtakingly popular in medieval England — carried by kings, saints, and peasants alike — that its pet form 'Jack' became essentially synonymous with 'any ordinary man'. By the 14th century, it had slipped free of its role as a proper name entirely.
From that leap — from a person to a type of person — everything else followed. A 'jack' came to mean a common labourer, a working man, a fellow of no particular distinction. This sense survives in phrases like 'lumberjack' (a man who cuts lumber) and 'steeplejack' (a man who climbs steeples), as well as the expression 'every man jack', meaning every single person without exception. The word carried a democratic, slightly rough-edged energy — it was the name of the people, not of the powerful.
The leap from 'common man' to 'labour-saving device' is one of the most fascinating in English word history. By the late 15th and early 16th centuries, any mechanical device that replaced the work of a human servant began to be called a 'jack'. A 'roasting jack' was a mechanical spit-turner that replaced the kitchen boy who used to sit by the fire doing that tedious job by hand. The same logic gave us the 'bootjack', a device for pulling off boots without needing a servant to kneel and tug. The car-lifting 'jack' that we know today belongs to this long tradition — a machine doing the work an ordinary man would otherwise do.
The word spread its roots in every direction. In card games, the 'jack' — the knave — is the lowest of the face cards, once again representing the common man beneath the queen and king. The small ball aimed at in the game of bowls is called a 'jack', likely because it represents the smallest, humblest target. Even in electrical sockets, the 'jack' (as in a headphone jack) preserves the idea of a small, practical connector — an unassuming but essential device.
Some of the word's relatives are surprising. 'Flapjack', 'crackerjack', and 'hijack' all carry the syllable, though their connections to the original sense vary. 'Hijack' is thought to come from the command 'high, Jack!' — an order to raise one's hands — spoken by American highway robbers in the early 20th century. 'Blackjack', the card game and the weapon, both trade on the word's sense of something common, tough, and a little dangerous. Even the name 'jackpot' — now meaning a huge prize — originally referred to a pot in poker that could only be opened by a player holding a pair of jacks or better.
What makes 'jack' so remarkable is its sheer democratic vitality. It started as the most common man's name in England, shed its capital letter, and proceeded to colonise the language in dozens of directions — naming tools, games, animals, plants, and idioms. The humble John became the humble jack, and the humble jack became almost everything. Few words in English have done so much work so quietly.