noun

• (historical) A small container containing flint, steel, and tinder (dry, finely-divided fibrous matter), once used to help kindle a fire.
  "Haines helped himself and snapped the case to. He put it back in his sidepocket and took from his waistcoatpocket a nickel tinderbox, sprang it open too, and, having lit his cigarette, held the flaming spunk towards Stephen in the shell of his hands."
• (by extension) A place that is so dry and hot that there is danger of fire.
  "And then came the night that made America famous / Was it carelessness or someone's sick idea of a joke? / In the tinderbox trap that we hippies lived in, someone struck a spark"
• (figurative) A potentially dangerous situation.
  "This act was the "match that ignited the great tinderbox of fuel" that had been building for years between many of the countries in Europe."