from
The Collaborative International Dictionary of English v.0.48
backfire \backfire\, back fire \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.
[Webster 1913 Suppl.]
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.
[Webster 1913 Suppl. +PJC] Backfire