1、business的基本意思是指某人为谋利(尤为自己)的“日常工作”或“职业”,引申可表示“职责,事务”。business现在多用来指“商业,生意,贸易”(不可数),引申可表示“商店,商行”(可数)等。business还可用来表示“演员舞台的动作、表情等”,作“怪事,勾当”解时常用作贬义。
4、inbusiness指“在经商营业”,属于形容词短语或状语短语范畴;onbusiness指“因事或因公,出差”,属于状语短语。
He does wholesale business, while his brother is engaged in retail business.

