Today Jack is a proper name. But earlier it was used in English as the pet form of the name John. As a first name Jack was already so common in the Middle Ages that it became the general term for «man» or «boy». Furthermore, it became part of terms like «jackpot», which we still know today. In other words, whether a gambling grand prize (jackpot) or the frequency of the first name: Who is called Jack, «likes to get to the point», just like our plant for men.

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Perhaps this also applies to the well-known namesakes, such as: actor and Oscar-winner Jack Lemmon; actor and Oscar-winner Jack Nicholson; and co-founder of the microblogging service Twitter, Jack Dorsey.