noun
winning tile
In mahjong, the tile that completes a player's hand and allows them to declare a win.
彼は最後の上がり牌を引いて、見事に和了った。
He drew the winning tile and won the hand brilliantly.
上がり牌を捨ててしまわないように注意してください。
Be careful not to discard the winning tile.
Compound of 上がり (agari, 'winning', from 上がる 'to rise, to finish') and 牌 (hai, 'tile'). The reading ハイ is the on'yomi of 牌, commonly used in mahjong terminology.