"A figment of your imagination" refers to something that is purely imaginary and has no basis in reality. There are a few synonyms for this phrase that can be quite useful when expressing the same idea. One such synonym could be "fantasy," which refers to something that is imaginary or unrealistic. Another synonym could be "delusion," which implies a mistaken belief that something is real when it is not. A third synonym is "hallucination," which refers to a perception of something that isn't actually present. Overall, these synonyms are useful when trying to communicate the idea of something being imaginary or not real to someone else.