a toss-up; a toss up （決勝負的）擲錢幣；[口]勝負各半的機會；一半的機會；難以決定的事；很難肯定的事情

tossup （决定某事的）擲錢；一半的機會
toss up 一下子做好[燒好]（菜等）；擲錢(以決定某事)；[口]嘔吐

例句：

The election was a toss-up, the winner still hasn't been determined. 這場選舉勝負難分,截至目前還不知鹿死誰手。