chick·en·pox or chicken pox 
(chĭkən-pŏks′)
(chĭkən-pŏks′)n.
An acute contagious disease, primarily of children, that is caused by the varicella-zoster virus and characterized by skin eruptions, slight fever, and malaise. Also called varicella.
[Perhaps in allusion to the mildness of the disease as contrasted with smallpox.]