noun
captured piece (shogi)
In shogi, a piece taken from the opponent that can be placed back on the board as one's own.
持ち駒の歩を打って王手をかけた。
I dropped a captured pawn and put the king in check.
noun
reserve; asset held in reserve
Figurative use: a person, object, or resource kept ready for future use, like a shogi piece in hand.
He is a reserve asset for the company, someone who can be placed in an important position at any time.
このデータは交渉の持ち駒になる。
This data will be a bargaining chip in the negotiations.
Compound of 持ち (mochi, 'holding') + 駒 (koma, 'piece'). Originally a shogi term for a captured piece held in hand, later extended figuratively to any reserve resource.