Why is Jack short for John?

The nickname "Jack" for John is a historical development that dates back to the Middle Ages. It is believed to have originated from the diminutive form "Jankin" or "Jackin," which was a common way to create nicknames at the time. The suffix "-kin" was added to names to create a diminutive or affectionate form, much like "-chen" in German. Over time, "Jankin" became "Jackin," which was eventually shortened to "Jack." This practice was not unique to the name John; it was a common way to create nicknames during that period.

Additionally, the name John was once used as a generic name for English commoners and peasants (John Doe), which could be another reason why "Jack" became a common nickname for John. The name Jack was also used as a general term to refer to any man, especially of the common classes, which may have contributed to its widespread use as a nickname for John.