Definition
to subtract a specific amount from a price
扣除一定的數額（從價格中）
If you buy this item today, I can knock fifty dollars off the price.
如果你今天購買這件商品，我可以從價格中扣除五十美元。
She asked the clerk to knock a certain amount off her order.
她要求店員從她的訂單中扣除一定金額。
To promote sales, the store decided to knock off one-tenth of the original price.
為了促銷，商店決定從原價中扣除十分之一。