There are several synonyms for the term "complementary minor" in music theory. One such synonym is "relative major," which refers to the major key that shares the same key signature as the complementary minor. Another synonym is "parallel minor," which refers to the minor key that has the same tonic note as the corresponding major key. Additionally, some might use the term "natural minor" to refer to the complementary minor, as it is often the natural scale built on the sixth degree of the relative major scale. Regardless of the terminology used, understanding the relationship between major and minor keys is an essential component of music theory and composition.