If you’ve read a series of four books, or watched four movies made as a set, you’ve experienced a tetralogy. This word comes from the Greek “tetra,” meaning “four,” and the suffix “-logy,” which indicates an interest or topic of study. In ancient Greece, tetralogies were presented in competition at Dionysiac festivals, which were the foundation for the Greek theater tradition. Dramatists would compete with three tragedies, followed by a satyr play, a drama containing “swift action, vigorous dancing, boisterous fun, and much indecency in speech and gesture,” according to one classical theater guide.