【Accident】

1）an unpleasant event, especially in a vehicle, that happens unexpectedly and causes injury or damage （可数名词）；（交通）事故；意外遭遇；不测事件

例：He was killed in an accident. 他死于一次车祸。
One in seven accidents is caused by sleepy drivers. 每七次交通事故就有一次是驾车者困倦造成的。

2）something that happens unexpectedly and is not planned in advance （可数或不可数名词）意外；偶然的事

例：Their early arrival was just an accident. 他们早到仅仅是偶然而已。
It is no accident that men fill most of the top jobs in nursing. 男人担任护理中大多数最重要的工作绝非偶然。

【拓展】by accident ： it happens completely by chance 偶然，意外的

如： We met by accident at the airport.
我们在机场不期而遇。