misfire; failure to fire
Used for guns, explosives, or engines that fail to ignite or fire. Also used metaphorically for plans or efforts that fail to materialize.
銃が不発に終わった。
The gun misfired.
The firework failed to go off, and the audience sighed.
計画は不発に終わった。
The plan fizzled out.
空振り literally means a swing-and-miss and is used for an effort that produces no effect, while 不発 focuses on something failing to ignite or launch, whether literal or metaphorical.
成功 means a plan or attempt succeeds, the opposite of 不発, where it fails to fire or come to fruition.
不発 describes an explosive failing to go off, the opposite outcome of a successful 起爆.
不振 describes an ongoing slump or poor performance (e.g. a batter in a slump), whereas 不発 refers to a single failure to fire or produce an effect.
unexploded ordnance; UXO; unexploded bomb/shell
Compound of 不 (fu, 'not') and 発 (hatsu, 'discharge' or 'fire'). The reading ふはつ follows standard on'yomi.