One possible synonym for the term "theme and variations" is "rhapsody." This term refers to a composition that features a recurring theme, often in a free-flowing and improvisational style. Another possible synonym is "medley," which describes a musical mash-up of different melodies or themes. A "potpourri" could also be used to describe a combination of different themes or variations. The term "adaptation" could also be used to refer to a rearrangement of a theme to suit a different musical context. Whatever term is used, it's important to note that the concept of theme and variations is a timeless one that has been used by composers for centuries to create complex and memorable works of music.