導どう火か線せん

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Meanings

fuse; blasting fuse

A cord or line that carries fire to an explosive device. Also used metaphorically for something that triggers a larger event.

導どう火か線せんに火ひをつけるto light the fuse
彼かれは導どう火か線せんに火ひをつけてすぐに逃にげた。
He lit the fuse and immediately ran away.
〈事こと〉が導どう火か線せんとなるfor something to become the trigger (of a larger event)
小ちいさな衝しょう突とつが長ながい戦せん争そうの導どう火か線せんとなった。
A small clash became the trigger for a long war.
導どう火か線せんが短みじかいto have a short fuse (quick to anger)
彼かれは導どう火か線せんが短みじかいから、すぐに怒おこり出だす。
He has a short fuse, so he gets angry right away.

引ひき金がねN1
引き金 literally means the trigger of a gun and is used metaphorically for something that sets off an event, while 導火線 literally means a fuse and is used the same way, but 導火線 more often implies a slow build-up before the explosion.
起き爆ばく剤ざい
起爆剤 is literally a detonating agent and is used metaphorically for a catalyst that spurs sudden change, similar to the figurative use of 導火線 but with less sense of a delay before the effect.
火ひ種だね
導火線 (literally 'fuse') emphasizes the trigger that sets off an already-building explosion, while 火種 focuses more on the underlying source that could flare up.

信しん管かん
信管 is the detonator or fuze mechanism inside a shell or bomb, while 導火線 is the burning cord that carries fire to the explosive, so the two are different parts of the same device.

本ほんN5
book; volume; script · this; present; current; in question · main; head; principal · real; genuine; regular; proper · counter for long cylindrical objects; counter for films, TV shows, etc.; counter for goals, home runs, etc.; counter for telephone calls

Compound of 導 (guide, lead) + 火 (fire) + 線 (line, wire). The word literally means 'fire-guiding line'.