Aeschylus trilogy
I believe the answer is:
oresteia
'aeschylus trilogy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oresteia that I've seen before include "three tragedies for Aeschylus" , "Play trilogy by Aeschylus, see a riot (anag.)" , "Aeschylus's play trilogy" , "Greek plays" .)