verb

• (of a gun, cannon, Bunsen burner, etc., intransitive) To fire in the opposite direction, for example due to an obstruction in the barrel.
• (of a reciprocating engine, intransitive) To experience a premature ignition of fuel or an ignition of exhaust gases, making a popping sound.
  "It was just after the Biafran war, and all the local people were still jumpy. Any time a car backfired or a police siren howled, they would dive under desks or tables instinctively."
• (idiomatic, transitive) To fail in a manner that brings down further misfortune.
  "His attempt to make money by importing luxury cars backfired horribly when fuel prices tripled."
• (firefighting) To set a back fire (small, controlled fire to limit spread of a larger fire).

noun

• (firefighting) Alternative spelling of back fire.