noun
gunpowder magazine; explosives warehouse
Literal storage facility for gunpowder or explosives.
その火薬庫は厳重に警備されていた。
The gunpowder magazine was heavily guarded.
noun
powder keg
Figurative use for a volatile situation that could easily explode into conflict.
その地域は民族対立の火薬庫だ。
That region is a powder keg of ethnic conflict.