tin ‧ der ‧ box /ˈtɪndəbɒks $ -dərbɑːks/ BrE AmE noun
1 . [countable usually singular] a place or situation that is dangerous and where there could suddenly be a lot of fighting or problems:
The area is a tinderbox that could again plunge the country into civil war.
2 . [countable] a box containing things needed to make a flame, used in the past