Meaning
Respond to an attack by using a similar method as one's attacker.
Origin
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...
