A fixed amount is a predetermined quantity of something that does not change. It is often used in reference to money, where it is known as a fixed RATE or fixed UNIT. The crossword solutions for the term 'fixed amount' are 'RATE' (4 letters) and 'UNIT' (4 letters). RATE is a term used to describe the amount of money charged for a service or product, while UNIT is a term used to describe a single item or quantity of something.