An accident is an unfortunate incident (event), such as a car crash, or an unexpected event - such as winning the lottery. An incident is a single distinct even or occurrence, and it can also be a public disturbance - such as a riot. An accident - Refers to the event. It is an unplanned, undesired event in a sequence of events that causes an unintended injury, death or property damage. An incident is an undesired event that may cause personal harm or other damage.

最简单的理解，incident 是“事件”而 accident 是“事故”。 accident 强调的是一种“意外情况”或者“意料之外”，很多时候有种“飞来横祸”的味道，比如我们常用的He had a car accident（他遇上车祸了），这种事情往往是我们不希望发生或者难以预料的。 incident 偏重于理解为一个独立的事件，这个事件可能是一种难免会发生的事，比如说球类比赛上的严重受伤，都用incident；另一种解释是突发事件，比如说某国发生政变了，历史上发生的什么事变之类的，也用这个词。 但愿对你有帮助吧

How? You find an English-Chinese dictionary, and you look'em up.