What is the greek word for symphony?

There isn't a single perfect Greek word translation for "symphony" in the modern sense of a musical composition. The word "symphony" itself comes from Greek: συμφωνία (symphonía).

However, συμφωνία (symphonía) in ancient Greek referred more broadly to a "harmony" or "agreement" – it could describe a concord of sounds, but also a concord of opinions or actions. It wouldn't necessarily imply the specific structure of a modern symphony.