Definitions
1.verbTo make proof against bullets.
2.verbTo make resistant to failure."We have to bulletproof this program before we let the users at it; check every input, catch every possible flaw...it must not fail in use."
3.adjective(of a material) Capable of withstanding a direct shot by a bullet fired from a gun."A bulletproof window."
4.adjectiveReliable, infallible, sturdy or error-tolerant.
5.adjective(usually of an idea or concept) Unbreakable, very tough.