Chicken Pox

“Chicken pox,” which, to reiterate, has nothing to do with chickens, is a virus more precisely known as Varicella zoster, a member of the herpes family.  Chicken pox is a very common childhood disease that produces itchy bumps (“pocks” or “pox”) on the skin and can be very unpleasant for a week or two.  But while chicken pox can produce serious complications in adults (especially pregnant women), most cases resolve themselves fairly quickly and thereafter confer lifelong immunity to the disease.

The relative mildness of chicken pox is striking in contrast to another “pox” disease, smallpox, probably the deadliest disease in human history before it was eradicated (at least “in the wild”) in the 1970s.  This contrast probably explains the name “chicken pox,” which connotes mildness and safety as opposed to the virulence of smallpox.  It has also been suggested that “chicken” in the name refers to a supposed resemblance of the pox to chickpeas, or that the skin of a sufferer looks as if it has been pecked by chickens.  But the “not dangerous” sense of “chicken” is the most likely source, especially given that chicken pox was for many centuries considered an innocuous form of the deadly smallpox. ~ The Word Detective
http://www.word-detective.com/