Tetralogy \Te*tral"o*gy\, n. [Gr. ?; te`tra- (see Tetra-) + ? a speech, discourse: cf. F. t['e]tralogie.]

(Gr. Drama) 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 Revised Unabridged Dictionary (1913)