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. The tool matters a great deal to him. 工具对他来说极其重要。
2. It does not matter which you choose. 不论选择哪一个，都无关紧要。
3. I denounce his silence on this matter. 我谴责他对这件事情的沉默。
英英解释
n.
1. that which has mass and occupies space
2. a vaguely specified concern
3. some situation or event that is thought about
4. a problem
5. (used with negation) having consequence
6. written works (especially in books or magazines) v.
1. have weight; have import, carry weight
