<p><strong>Verb</strong></p><ul><li>(used without object) to have a loud, premature explosion in the intake manifold (of an internal-combustion engine)</li><li>to bring a result opposite to that which was planned or expected: The plot backfired</li><li>to start a fire deliberately in order to check a forest or prairie fire by creating a barren area in advance of it</li></ul><p><strong>Noun</strong></p><ul><li>(in an internal-combustion engine) premature ignition of fuel in the intake manifold</li><li>an explosion coming out of the breech of a firearm</li><li>a fire started intentionally to check the advance of a forest or prairie fire</li></ul>