ace up one's sleeve; trump card; last resort
A hidden resource, plan, or skill kept in reserve for a decisive moment. Often used when someone reveals a final, powerful move.
彼は交渉の最後に奥の手を出した。
He played his trump card at the end of the negotiation.
I still have a last resort to solve this problem.
secret skill; hidden technique
Refers to a special, often esoteric, technique or knowledge not shared openly. Common in contexts like martial arts, crafts, or professional expertise.
The craftsman teaches his secret techniques only to his apprentices.
Archaic literal meaning. In modern Japanese, 左手 (ひだりて) is used instead.
In old documents, 奥の手 can refer to the left hand.