accident
n.
意外； 偶然事故
John's had an accident:he's been knocked down by a car.
约翰出事了,他被一辆小汽车撞倒了.
by accident
偶然；无意中：
I met Jacob by accident in the cinema.
我偶然在电影院遇到了雅各布.
An accident happened to the washer.
冼衣机出了故障.