A Jack or Knave, in some games referred to as a bower, is a playing card which, in traditional French and English decks, pictures a man in the traditional or historic aristocratic or courtier dress, generally associated with Europe of the 16th or 17th century. The usual rank of a jack is between the ten and the queen.
The earliest predecessor of the knave was the thānī nā'ib (second or under-deputy) in theMamlukcard deck. This was the lowest of the three court cards and like all court cards was depicted through abstract art or calligraphy. When brought over to Italy and Spain, the thānī nā'ib was made into an infantry soldier or page ranking below the knight card. In France, where the card was called the valet, the queen was inserted between the king and knight. The knight was subsequently dropped out of non-Tarot decks leaving the valet directly under the queen. The king-queen-valet format then made its way into England.
As early as the mid-16th century the card was known in England as the knave which originally meant 'boy or young man', as its German equivalent, Knabe, still does. In the context of a royal household it meant a male servant without a specific role or skill; not a cook, gardener, coachman, etc. The French word valet means the same thing. Knave became a derogatory word because royal households had so many of these young men who went swaggering around the streets picking fights, molesting girls and generally making nuisances of themselves. It evolved to mean 'young manservant or henchman'.[1]
The German nickname of Bauer ("farmer" or "peasant") often used for the Jacks, appears in English as the loanword, Bower, used for the top trumps (usually Jacks) in games of the euchre family as well as some games of German origin where the Jacks play a significant role e.g. Reunion.
The word 'Jack' was in common usage in the 16th and 17th centuries to mean any generic man or fellow, as in Jack-of-all-trades (one who is good at many things), Jack-in-the-box (a child's toy), or Jack-in-the-Pulpit (a plant).
The Knave of Hearts appears as a thieving antagonist in the traditional children's poem The Queen of Hearts
Jack = Bauer = Valet
J = B = V