In the latest installment of Danny Gregory's The Peanut Chronicles, he and PL tell the Ohio relatives about the pregnancy--antics ensue--and contemplate names:
We already have three Jacks. Jack Waldman was a friend of Patti's, a musician, who died just a month before PL and I met; she has always believed that he sent me to the party where I met her. (Actually, I took a cab.) Jack Buchanan is one of our favorite British actors, and, of course, the baby was conceived in an Atlantic City Jacuzzi.Peanut: Dead Rabbit and Beyond (November), Part II [themorningnews.org]
Jack, it turns out, was a popular name until the 1920s and isn't used much these days in America. [ummm, I, er, you don't-- never mind. -greg] It's usually short for John or Jacob or Jake. It has nothing to do with FrĖre Jacques. One book says the name means "God has been gracious" while another, ominously, defines it as "supplanter."