trilogy
n.
series of three related works, 1660s, from Greek trilogia "series of three related tragedies performed at Athens at the festival of Dionysus," from tri- "three" (see three) + logos "story" (see logos).
〔李〕[tri-=three三;logy=story故事 →] n.a group of three novels,plays or operas which form a related series(小说、戏剧等)三部曲
〔李〕[tri=three三;-logy n.=speech说话,叙述→“discourse in three sections分成三个部分的叙述”→] n. group of three related literary or operatic works(小说或戏剧的)三部曲