preventive

adj

1. Preventing, hindering, or acting as an obstacle to.

   “...and I sometimes think whether, like the ancient king, it would not be prudent to make an offering to destiny, and throw my set of emeralds into the lake." Emily could not but deprecate the emeralds being destined to any such preventive service;...”

2. Carried out to deter military aggression.
3. Slowing the development of an illness; prophylactic.

   “Physick is either curative or preventive.”

4. (obsolete)Going before; preceding.

   “Any previous counsel or preventive understanding.”

noun

1. (dated)A thing that prevents, hinders, or acts as an obstacle to.

   “Dogs should be warmly but airily housed; heartily, but not heatingly, fed — old Indian meal, mixed with oatmeal, suppawn, is the best general food, with a small quantity of salt, which is a preventive against worms […]”

2. (dated)A thing that slows the development of an illness.

   “Eaten with sugar yaourt is very palatable and refreshing in warm weather and is said to be a preventive of fever.”

3. A contraceptive, especially a condom.