any of the various Greek festivals in honor of Dionysus, esp. those at Athens from which the Greek drama originated
See Dionysia in American Heritage Dictionary 4
(dīˌə-nĭzˈē-ə, -nĭzhˈē-ə, -nĭsˈē-ə)
plural noun
Ancient Greek festivals held seasonally, chiefly at Athens, in honor of Dionysus, especially those held in the fall and connected with the development of early Greek drama.