also: しぶさく
noun
tetralogy; four-part work
Refers to a creative work consisting of four parts, such as a series of four novels, films, or plays.
この小説は四部作の第一巻です。
This novel is the first volume of a tetralogy.
映画の四部作を一気に観た。
I watched the film tetralogy in one sitting.
Compound of 四 (four) + 部 (part) + 作 (work). The reading よんぶさく uses the native Japanese reading for 四, while しぶさく uses the Sino-Japanese reading.