Fixed interest, or a fixed rate of interest, is a term that refers to a financial instrument or loan where the interest rate is agreed upon and remains the same throughout the term of the investment. Some common synonyms for fixed interest include absolute certainty, unvarying, invariable, inflexible, steadfast, steady, firm, stable, and unchanged. These synonyms highlight the key attributes of fixed interest and emphasize its predictable and reliable nature. In contrast, variable interest refers to an interest rate that fluctuates with the market and is subject to change over time. When considering investment options, it is important to weigh the pros and cons of both fixed and variable interest rates.