请问，有谁知道关于日本将棋中的piece in hand怎么翻译啊？

就是指“吃子利用”。是指已方可以把在对局中吃到的对方棋子，在形势需要时，投入棋盘中成为已方棋子而加以利用。

The captured becomes a piece in hand for the side that captured it.
直译：被“吃掉”的那个棋子就成为吃掉对方棋子那一方手中的棋子。

Captures
A captured piece is removed from the board and is held by the capturing player. The held piece (which is said to be 'in-hand') may subsequently be 'dropped' back into play on the side of the player who made the capture.

这是中文的将棋玩法详解：http://game.xicn.net/item/2006/12/19/308116.html

这是英文鸟将棋玩法：http://www.chessvariants.com/shogivariants.dir/tori.html

你可以对照着看。

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