The Collaborative International Dictionary
Tinder box
Tinder \Tin"der\, n. [OE. tinder, tunder, AS. tynder, tyndre; akin to tendan to kindle, D. tonder tinder, G. zunder, OHG. zuntara, zuntra, Icel. tundr, Sw. tunder, Dan. t["o]nder. See Tind.] Something very inflammable, used for kindling fire from a spark, as scorched linen.
German tinder. Same as Amadou.
Tinder box, a box in which tinder is kept.
Wiktionary
tinder box
n. (alternative spelling of tinderbox English)