The word "zappeion" is a specific term that refers to a specific building located in Athens, Greece. However, there are some synonyms for this term that can be useful for describing similar structures or locations. Some possible synonyms might include "exhibition center", "convention hall", "event space", or "trade show venue". These terms all describe places where large gatherings of people can come together for events, exhibitions, or other gatherings. While they may not be exactly the same as a "zappeion", they share some similarities and may be useful for describing similar places in other locations around the world.