preventative

adjective

1. Intended to prevent: deterrent, preclusive, preventive. See allow/prevent.
2. Defending against disease: preventive, prophylactic, protective. See allow/prevent.

The noun has 3 meanings:

Meaning #1: remedy that prevents or slows the course of an illness or disease
  Synonyms: preventive, prophylactic

Meaning #2: any obstruction that impedes or is burdensome
  Synonyms: hindrance, hitch, preventive, encumbrance, incumbrance, interference

Meaning #3: an agent or device intended to prevent conception
  Synonyms: contraceptive, preventive, contraceptive device, prophylactic device, birth control device

The adjective preventative has 2 meanings:

Meaning #1: tending to prevent or hinder
  Synonym: preventive

Meaning #2: preventing or contributing to the prevention of disease
  Synonyms: preventive, prophylactic