noun, plural te·tral·o·gies.
Examples from the Web for tetralogy
He saw what was happening there with regard to matters of art, and that he could not dream of producing his tetralogy.Wagner at Home|Judith Gautier
The work of Gringore, just noticed, forms part of such a tetralogy.A Short History of French Literature|George Saintsbury
Wagner never tired of exploiting the variation form in his operas, particularly in the Tetralogy.Beethoven|George Alexander Fischer
The drama itself comes second in the tetralogy of the Ring, being preceded by the Rheingold.
But this latter is more properly to be considered as the overture to a trilogy than as the first drama of a tetralogy.