From The Collaborative International Dictionary of English v.0.48:
Cowpox \Cow"pox`\ (-p[o^]ks`), n. (Med.)
A pustular eruptive disease of the cow, which, when
communicated to the human system, as by vaccination, protects
from the smallpox; vaccinia; -- called also kinepox,
cowpock, and kinepock. --Dunglison.