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. This matter concerns all of us. 这件事与我们每个人都有关系。
2. Her unique concern was her own comfort. 她唯一关心的是自己的舒适。
3. Therefore, we must concern "vacancy rate" of the data. 因此，当前必须关注“空置率”这个数据。
英英解释
n.
1. something that interests you because it is important or affects you
2. an anxious feeling
3. a commercial or industrial enterprise and the people who constitute it
4. something or someone that causes anxiety; a source of unhappiness
5. a feeling of sympathy for someone or something v.
1. have to do with or be relevant to
2. be on the mind of
