Pronunciation: (vak-sēn' or, esp. Brit., vak'sēn, -sin),[key] —n. 1. any preparation used as a preventive inoculation to confer immunity against a specific disease, usually employing an innocuous form of the disease agent, as killed or weakened bacteria or viruses, to stimulate antibody production.
2. the virus of cowpox, used in vaccination, obtained from pox vesicles of a cow or person.
3. a software program that helps to protect against computer viruses, as by detecting them and warning the user.
—adj. 1. of or pertaining to vaccination.
2. of or pertaining to vaccinia.
3. of, pertaining to, or derived from cows.