back·fire /-ˌfaɪr/
 逆火,回火,放火(vi.)放逆火,預先放火,發生意外
 backfire, back fire.
 1. A fire started ahead of a forest or prairie fire to burn only against the wind, so that when the two fires meet both must go out for lack of fuel.
 2.  (a) A premature explosion in the cylinder of a gas or oil engine during the exhaust or the compression stroke, tending to drive the piston in a direction reverse to that in which it should travel; also called a knock or ping. (b) an explosion in the exhaust passages of an internal combustion engine.
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 Back·fire Back-fire, v. i.
 1. Engin. To have or experience a back fire or back fires; -- said of an internal-combustion engine.
 2.  Of a Bunsen or similar air-fed burner, to light so that the flame proceeds from the internal gas jet instead of from the external jet of mixed gas and air. -- Back-fir*ing, n.
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 backfire
      n 1: a loud noise made by the explosion of fuel in the manifold
           or exhaust of an internal combustion engine
      2: a miscalculation that recoils on its maker [syn: boomerang]
      v 1: have an unexpected and undesired effect; "Your comments may
           backfire and cause you a lot of trouble" [syn: backlash]
      2: emit a loud noise as a result of undergoing a backfire; "My
         old car backfires all the time"
      3: set a controlled fire to halt an advancing forest to prairie
         fire