Well, there simply isn't enough documented evidence to let us know for sure, the best theory I've read is that the Middle English language had the words “Yicche” or “Icchen” meaning, “to itch.” The Old English word for “to itch” is “Giccan.” So it seems possible that “Chicken Pox” may simply be a bastardized version of “Giccan/Yicche/Icchen/Itching” + “Pox.”