There are several synonyms for the phrase "round number," which is used to describe a whole number that is easy to remember or work with. One alternative term is "even number," which refers to a number that is divisible by two without leaving a remainder. Another synonym is "whole number," which describes a number that is not a fraction or decimal. A third option is "integer," which is a number that can be positive, negative, or zero, but is not a fraction or decimal. Finally, "milestone number" is another term that can be used for a round number, as it marks a significant point in a series or sequence of numbers.