1. 首先down有降低的意思比如：knock down: 降價、下跌：
例子：
The market might abandon the stock, and knock down the price.
市場可能會拋售股票，從而令其股價下跌。
2. knock down還有倒下的意思：
He was knocked down by a car.
他被車撞到了。
The suspect was gunned down by the police.
嫌疑人被警察擊倒了。
3. down在動詞詞組裡面還有阻止、抑制的意思。
比如turn down:
I turned down the job offer.
我拒絕了這個工作機會。
4. down在動詞詞組裡面還有不工作的意思。比如：
The computer breaks down occasionally. We need to buy new ones.
電腦經常壞，我們需要買新的。
I need to shut down the computer and take a nap.
我要關電腦休息會兒。
5. down： 心情壓抑
The weather is getting me down.
這個天氣讓我很不開心。
6. 侮辱、低看一眼
He looks down on her and doesn't show any respect to her.
他看不起她而且很不尊敬她。
I cannot believe that she puts him down like that.
我不敢相信她如此的揶揄他。