from The American Heritage® Dictionary of the English Language, 4th Edition
- 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.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A common childhood disease caused by the varicella-zoster virus (VZV), also known as human herpes virus 3 (HHV-3).
Perhaps in allusion to the mildness of the disease as contrasted with smallpox.(American Heritage® Dictionary of the English Language, Fourth Edition)
chicken + pox (Wiktionary)