Definition
to subtract a specific amount from a price
扣除一定的数额（从价格中）
If you buy this item today, I can knock fifty dollars off the price.
如果你今天购买这件商品，我可以从价格中扣除五十美元。
She asked the clerk to knock a certain amount off her order.
她要求店员从她的订单中扣除一定金额。
To promote sales, the store decided to knock off one-tenth of the original price.
为了促销，商店决定从原价中扣除十分之一。