Definition of "Backfire" :

noun: a miscalculation that recoils on its maker

noun: a fire that is set intentionally in order to slow an approaching forest fire or grassfire by clearing a burned area in its path

noun: a loud noise made by the explosion of fuel in the manifold or exhaust of an internal combustion engine

noun: the backward escape of gases and unburned gunpowder after a gun is fired

verb: set a controlled fire to halt an advancing forest to prairie fire

verb: emit a loud noise as a result of undergoing a backfire

"My old car backfires all the time."

verb: come back to the originator of an action with an undesired effect

"Your comments may backfire and cause you a lot of trouble."