What is the origin of the word vaccine?

The terms vaccine and vaccination are derived from Variolae vaccinae (smallpox of the cow).

Dr. Edward Jenner coined the word vaccine in 1846, following his observation that milkmaids were protected from smallpox. Dr. Jenner discovered that exposure to the bovine form of smallpox (cowpox) - from blisters on the cows udder - educated the immune system on how to fight smallpox, a related virus. This discovery paved the way for modern vaccines, which act in a similar manner.