Does anyone know how Jack came to be a nickname for John?

I’ve wondered this myself. There are actually quite a few conventional nicknames that do not look like obvious derivatives of the given name. Here are a few that I can think of just offhand:

Bill or Billy for William
Bob or Bobby for Robert
Ned or Ted for Edward
Dick for Richard
Peggy for Margaret
Sally for Sarah
Nancy for Anne

I don’t think the idea of being “short” for something is as significant as that it is considered a diminutive. Many diminutives (“kitty” for “cat,” “doggie” for “dog”) are actually longer, but they still convey the idea of littleness.

Well, at least Bill has the “ill” in it, Bob or Bobby has the “ob” in it, Ned or Ted has the ‘ed” in it but Sally for Sarah has always had me wondering as well, and I didn’t know that Nancy was a nickname for Anne. And yes, you are right about the diminutive vs. the shortened form. Annie is a diminutive for Ann or Anne and is longer than both of them. But bottom line, you don’t know the answer either, do you? :)

No, I don’t. I’m just agreeing with and reinforcing the question because I’ve been curious about the same thing from approximately the time that Jack Kennedy was serving as a U.S. Senator from Massachusetts.

I wonder because my grandfather was John and my uncle was John, Jr. but was always called Jack. And I was just teasing you about not knowing the answer. :) You know just about everything else.

Not even close, my friend! What there is to be known would fill an ocean, and what I know is a scant thimbleful. I just try hard to avoid exhibiting my ignorance as if I were proud of it.

I’ve always thought that Bill for William must have come from German-speaking people pronouncing the W as a V (as it is done in German). So, Will is “Vill”, and somewhere along the way it mutated to Bill.

I really have no idea! I do remember hearing a story about Abe Lincoln, while he was practicing law, stood in a courtroom and asked a fella named John Cass whether his friends called him “Jack” – and why doesn’t Abe just go ahead and refer to him henceforth as “Jack Cass”?

So, this particular diminutive must have been around for some time.

Just to throw another wrench into the works, I had an uncle Verlin who was called Gus and an aunt Marcella that was called Tish. ????

According to wikipedia in Old English when you add the the diminutive suffix “ken” to “Jan” you get “Janken” which later became “Jack”. “Jan” is pronounced like “John”.

Did you watch that Jackie O movie this weekend too?? She called JFK “Jack::

Consider the many nicknames for Elizabeth:

Beth, Betsy, Betty, Bets, Bitsy, Libby, Liddy, Liz, Lizzie, Lizbeth, Eliza, Liza…

There are so many, I’ve probably forgotten a few. Some of those nicknames make sense (Beth, Liz), but some of them really don’t.

It came from the pronunciation of the French equivalent of John. (Jacques: approx. pron. Jack.) It’s usage spread among the sailors of 17th and 18th centuries and eventually into the general populations in English speaking countries.

The French equivalent of John is Jean. I had always understood that Jacques is treated as the French equivalent of James.

@prescottman2008‘s explanation makes sense to me, being based in a diminutive in the first place.