Tetralogy
Pronunciation : Te*tral"o*gy
Part of Speech : n.
Etymology : [Gr. Tetra-) + t?tralogie.] (Gr. Drama)
Definition : Defn: A group or series of four dramatic pieces, three tragedies and one satyric, or comic, piece (or sometimes four tragedies), represented consequently on the Attic stage at the Dionysiac festival.
Note: A group or series of three tragedies, exhibited together without a fourth piese, was called a trilogy.
Source : Webster's Unabridged Dictionary, 1913