preventive

• preventative

prevent +‎ -ive

preventive (comparative more preventive, superlative most preventive)

1. Preventing, hindering, or acting as an obstacle to.
2. Carried out to deter military aggression.
3. Slowing the development of an illness; prophylactic.
   • Sir Thomas Browne

     Physic is either curative or preventive.

4. (obsolete) Going before; preceding.
   • Cudworth

     Any previous counsel or preventive understanding.

preventive (plural preventives)

1. (dated) A thing that prevents, hinders, or acts as an obstacle to.
   • 1856, Henry William Herbert, The Complete Manual for Young Sportsmen

     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. (nonstandard) A thing that slows the development of an illness.
3. A contraceptive, especially a condom.

• Many speakers prefer to use preventive in adjective senses and preventative in noun senses.

preventive

1. feminine plural of preventivo