Preventive

a. [Fr. préventif, It. & Sp. preventivo.] Tending to prevent; hindering the access of; as, a medicine preventive of disease. Browne.

Preventive service, the duty performed by the armed police in guarding the coast against smuggling. [Eng.]

n. 1. That which prevents; that which intercepts access or approach. 2. (Med.) An antidote previously taken to prevent an attack of disease.