"No such thing" refers to the idea that something doesn't exist or is not possible. There are several synonyms for this phrase. One alternative is "fiction," which suggests that the idea is imaginary or made up. Another is "myth," which implies that it is based on a story or legend rather than reality. "Illusion" could also be used to convey that the idea is an optical trick or deception. "Delusion" denotes that the idea is a mistaken belief or misconception. "Fallacy" implies that the concept is a false or erroneous notion. Each of these synonyms can provide a slightly different nuance depending on the context for which they're used.