Word of the Day:

: a series of four connected literary, artistic, or musical works

The Hitch Hiker's Guide to the Galaxy: A Trilogy in Four Parts (as it was published in England) is, as the name rather coyly intimates, a tetralogy of Douglas Adams novels. "Vintage has reissued Ford Madox Ford's Parade's End, a massive tetralogy of novels about England's cascading misfortunes during World War I." - From a review by Scott Eyman in Palm Beach Post (Florida), April 15, 2012

More example sentences

The original tetralogies were sets of four plays (three tragedies and a comedy) performed serially on the Athenian stages of ancient Greece. These sets of plays were similar to the "trilogy," a group of three serial Greek tragedies. The word "tetralogy" is from the Greek combining form "tetra-," meaning "four," joined with the combining form "-logia," which in turn comes from "logos," meaning "word." Other "tetra-" words include "tetrahedron" (a solid shape formed by four flat faces) and "tetrapod" (a vertebrate with two pairs of limbs).