Merriam-Webster Collegiate Dictionary - premunition

 noun  Etymology: Latin praemunition-, praemunitio strengthening of an argument to forestall objections, from praemunire to fortify in advance, from prae- + munire to fortify — more at munition  Date: 1607  1. archaic an advance provision of protection  2.  a. resistance to a disease due to the existence of its causative agent in a state of physiological equilibrium in the host  b. immunity to a particular infection due to previous presence of the causative agent