back·fire / ˈbakˌfī(ə)r/ • v. [intr.] 1. (of an engine) undergo a mistimed explosion in the cylinder or exhaust: a car backfired in the road.2. (of a plan or action) rebound adversely on the originator; have the opposite effect to what was intended: overzealous publicity backfired on her.• n. 1. a mistimed explosion in the cylinder or exhaust of a vehicle or engine.2. a fire set intentionally to arrest the progress of an approaching fire by creating a burned area in its path, thus depriving the fire of fuel.