Fact of the Day: Jack and John
Jack comes from the Middle English “Jankin”, Jan being a contracted form of Jehan, or John, and -kin being a diminutive suffix. Jankin with time became Jackin, and was later shortened simply to Jack. Additional information: [a slightly different version] “Jack is actually derived from the name Johannes, which was shortened to Jehan and eventually to Jan. The French were fond of tacking the suffix -kin onto many short names. French nasalization resulted in the new combination being pronounced Jackin instead of Jankin. The name Jackin was shortened to Jack.”

From On This Day