above board = If a plan or business agreement is above board, it is honest and not trying to deceive anyone.（计划或交易）光明正大的。
词源If card players keep their hands above the table (the board), other players can see what they are doing. 源于纸牌游戏。如果玩牌者将手放在桌上，其动作就会被其他玩牌者看得一清二楚。

【例句】
The deal was completely open and above board.
这笔交易完全是光明正大的。

She's been totally open and above board about it.
她以这事完全坦率、光明正大。