Why is the discount rate called the discount rate? It doesn't discount anything. On the contrary, it's about how much the central bank charges other banks to use its financial resources. Why isn't it called, for example, 'the basic interest rate' or 'the primary interest rate'? I can think of many better names.
Discount has a couple of economic meanings. One is a reduction in price in exchange for prompt payment:
The car is $2500 If you pay me cash today I'll give you a discount of $500 on the car.
Equivalently, and in technical use, a discount is a charge agreed in exchange for late payment
The car is $2000, but if you need a month to find the money, I'll charge a discount of $500.
This second use of discount is technical and probably wouldn't be used in a conversation about cars, but might be found in a textbook on economics.
The "Federal Reserve discount rate" is the rate at which the Fed charges discounts on short term loans to other banks.