In the late medieval period the jack was called the knave. A knave was then a male servant of royalty.The card came to be known as the jack during the middle of the 19th century, when card manufacturers began to label playing cards to indicate their value.The obvious confusion between "Kn" and "K" led to the renaming of the knave as the Jack. However, books of card games published in late victorian timesevidently still referred to the card as the "knave", and the term with this definition is still recognized in the UK.
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