Flat is a word that is often used to describe a surface that is even and level. However, there are many synonyms that can be used in place of this word, depending on the context. For instance, "level" is a synonym that is commonly used when describing a surface that is uniform in height. "Smooth" is another term that can be used to describe a surface that is flat and free of bumps or ridges. "Even" is also a synonym of "flat," which is often used to describe the uniformity of a surface. "Horizontal," "plane," and "straight" are some other synonyms of "flat" that can be used in different contexts.