n. 掷钱币, (成败各半的)相等机会
在线英汉词典

toss-up的短语、例句：

toss-up n 1 act of tossing a coin 掷硬币. 2 (infml 口) even chance 机会相等
Both players are equally good so it´s a toss-up (ie impossible to predict) who will win. 那两个运动员不相上下, 谁能取胜还很难说.