business end
noun
1- informal (the business end) the functional part of a tool or device〈非正式〉（工具、设备等）使用的一头, 锐利的一端：
he found himself facing the business end of six lethal-looking weapons.
他发现有六件杀人凶器对准着他。
1.1
- the essential or basic part of a process or operation（某一过程）不可或缺的组成部分：
the rigs are the business end of the oil industry.
钻塔是石油工业不可或缺的部分。