Definition of: vaccine

(vak′sēn, -sin) noun
1. The virus of cow-pox, as prepared for or introduced by vaccination: usually lymph, dried or fluid, or part of the crust from a pustule.
2. Any inoculable immunizing agent; a preparation containing bacteria so treated as to give immunity from specific diseases when injected into the subject.
—adjective
1. Pertaining to or derived from cows.
2. Pertaining to cowpox or vaccination. [<L vaccinus pertaining to a cow <vacca cow]