A tinderbox is a box of materials for starting a fire. Carry a tinderbox, open the tinderbox, the old tinderbox.
It held flint, steel and tinder together and was how every fire was lit before matches, which arrived in the 1820s. The figurative use is the live one: a tinderbox is any situation one spark would set off.
1nountinderboxA box of materials for starting a fire.
“The traveller took out his tinderbox and struck a spark to light the campfire.”
tinderbox is a box.
Tinder plus box, first recorded around 1530.
From tinder + box, first use appears c. 1530, in the writings of John Palsgrave.
Etymology from Wiktionary, CC BY-SA