1. affair的意思是“有关的事，事务，活动等”，如foreign affairs（外事），也常指婚外恋；

2. event指“每日里发生的事件，事或活动，比赛项目”；

3. incident同event意思相近，指“事件，事”，尤指较重大的、有影响的政治事件等。

例：They have no right to interfere in the domestic affairs of Iran.
他们无权干涉伊朗的内政。

The affair remained a complete mystery.
那件事至今还是个谜。

The important event of the week was the big storm.
那一周中的大事就是那场大暴风雪。

Coming events in the village include a dance-show and a treat for the school children.
村里即将发生的大事，就是招待学校的孩子们和舞蹈表演。

Our team won the silver medal in this event.
我们队获得该项目的银牌。

On the very day before I left, an incident occurred.
事件就发生在我要离开的当天。

There were several incidents on the frontier between the two nations in the 50s.
50年代两国边境发生了许多大事。