affair 含义较广，侧重指已发生或必须去做的任何事情或事务。复数形式多指重大或较复杂的事务。
business 通常指较重要或较难而又必须承担的事情，也可指商事。
matter 普通用词，着重指一件考虑中的或需要处理的事。
concern 往往强调与个人或团体利害有直接或重大关系的事。
thing 用作“事情”解时，词义较笼统、含糊，多用于指不很具体的事。
参考例句
1. For me, this is a happy thing. 对我来说这是一件幸福的事。
2. We should let them know this thing. 我们应该让他们知道这件事。
3. What is the thing that everybody has? 每个人都拥有的东西是什么？
英英解释
n.
1. a special situation
2. an action
3. an artifact
4. an event
5. a statement regarded as an object
6. any attribute or quality considered as having its own existence
7. a special abstraction
8. a vaguely specified concern
9. an entity that is not named specifically
10. a special objective
11. a persistent illogical feeling of desire or aversion
12. a separate and self-contained entity
