Respond to an attack by using a similar method as one's attacker.
When we 'fight fire with fire' we are likely to employ more extreme methods than we would normally do. That was also the case with the actual fire-fighting that was the source of this phrase. US settlers in the 19th century, who originated the phrase, attempted to guard against grass or forest fires by deliberately raising small controllable fires, which they called 'back-fires', to remove any flammable material in advance of a larger fire and so deprive it of fuel. This literal 'fighting fire with fire' was often successful, although the settlers' lack of effective fire control equipment meant that their own fires occasionally got out of control and made matters worse rather than better. One such failure was recorded in Caroline Kirkland's novel, based on her experiences of frontier Michigan in the 1840s, A New Home - Who'll Follow? Or, Glimpses of Western Life (written under the pseudonym of Mrs. Mary Clavers):
The more experienced of the neighbours declared there was nothing now but to make a "back-fire!" So home-ward all ran, and set about kindling an opposing serpent which should "swallow up the rest;" but it proved too late. The flames only reached our stable and haystacks the sooner,The method has continued to be used however and foresters now routinely create roads or unplanted areas to act as fire-breaks in woodland that is at risk of fire.
The term 'backfire' is now more often applied to plans that fail in a way that weren't intended. It wasn't used in that negative sense until the early 20th century and probably derives from the popping explosions that used to be commonly heard from the exhausts of faulty motor vehicles, not from forest 'back-fires' which ran out of control.
The earliest usage of 'fight fire with fire' that I've found in print is in the US author Henry Tappan's 1852 reminiscence A Step from the New World to the Old, and Back Again:
Smoking was universal among the men; generally cigars, not fine Havanas, but made of Dutch tobacco, and to me not very agreeable. I had some Havanas with me, and so I lighted one to make an atmosphere for myself: as the trappers on the prairies fight fire with fire, so I fought tobacco with tobacco.
The Phrase A Week newsletter goes out to 71,000 subscribers (53,000 by e-mail, 18,000 by RSS feed).
Definition of hayrick. : a relatively large sometimes thatched outdoor pile of hay : haystack.
(of a plan) to have the opposite result from the one you intended:
Her plans to make him jealous backfired on her when he went off with her best friend.backfire (MAKE NOISE)
(of an engine) to make a loud noise as a result of fuel burning too early:
I was woken by the sound of a truck backfiring.