伝でん家かの宝ほう刀とうを抜ぬく

expression, godan verb (-ku)

play one's trump card; use one's secret weapon

Idiomatic expression meaning to finally bring out one's most powerful or decisive resource, often after holding it in reserve. Literally 'to draw the treasured sword of the family'.

• 交こう渉しょうが難なん航こうしたので、ついに伝でん家かの宝ほう刀とうを抜ぬくことにした。

  Negotiations were difficult, so we finally decided to play our trump card.

• 彼かれはここぞという時ときに伝でん家かの宝ほう刀とうを抜ぬく。

  He brings out his secret weapon at the crucial moment.