Jack

Just in case anyone’s wondering why Jack has often been a nickname for John, it dates back to the Middle Ages, where kids named John would often get the nickname “Jenk” or “Jankin” / “Jenkin”. At some point this turned into “Jakkin” and finally, “Jack”, just in time for the little rascal to feature in a gazillion nursery rhymes and fairy tales like Jack and the Beanstalk.

The origin given is a frequent misunderstanding. This is the right etymology and history.

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Hebrew: Jacobus >>> Classical Latin "Jacobus" >>> French "Jacques" >>> English "Jack". The origin and history then is from Jacob (English)

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It is also equivalent to James and Jake.

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For interest: Jacobus (classic Latin) >>> Jacomus (modified late latin)>>> James. The standard translation of James into French is "Jacques". Which sounds like Jack if the pronunciation is anglicized.

I think it is possible that part of the reason Jack became common in England was through confusion with Jacques. However, that can't be the whole story because Jack is quite clearly used as a pet form of John, not James, in England. Is there any evidence that Jack was ever used as a pet form of James in medieval England? If not, then the derivation from Jackin/Jankin is surely also a part of the full history of this name.

Also used as a diminutive for Jacob.

I disagree with the statement that Jack and John are and have long been considered separate names. Jack has always been the diminutive of John. Traditionally among English speaking people, Jack was not used as a proper given name, but only as a nickname. It has only been in this century that, usually through ignorance, boys have actually been named Jack instead of John. Even the famous Jack's that are sighted were not named Jack. Jack London's name was John. Jack Kerouac's name was Jean-Louis. Jack Nicholson, Jack Kennedy, Jack Lemmon, Jack Hawkins, Jack Lord, Jack Warden, and Jack Straw were all named John and most other famous Jacks were named Jacob or another given name. Even Jack Russell terriers are named for a man named John Russell. I believe it would be difficult to find anyone before the 20th century actually named Jack on their birth certificate. It simply wasn't done, just as you don't name someone Jim instead of James or Bob instead of Robert or Dick instead of Richard. It has only been during the last few decades that many people seem to have forgotten this custom. This was commonly known by English speaking people and is still quite commonly known, even in popular culture. For instance in the film "Scent of a Woman" Al Pacino makes a joke that he knows Jack Daniels so well he calls him John, indicating a reverse formalizing of the commonly known nick name. This did not need explaining in the film, it was understood. Jack is commonly used in nursery rhymes and old slang because it is the informal, familiar version of John, one of the most common names in the English language throughout history. [noted -ed]

Middle English Jakke, borrowed from Low German and Dutch pet forms "Jankin" and "Jackin", which come from "Jan" (the German version of John). "Jankin" meaning literally "Little John". The surname "Jenkins" also derives from "Jankin". Occasionally Jack is derived as an Anglicization of similar-sounding Jewish names.

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There is a theory that says Jack has been used in Britain for a much wider selection of traditionally English names. Two volumes; "The kinship of Jack, I & II" by Peter McClure of the University of Hull, describe it as a pet-form of Middle English personal names with the suffixes -kin, -ke, -man, -cot, -cus and -cok".