tri-, three, -log, to say, dialogue, 語源はdialogue, tetralogyと同じ。
英語の語源
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).
例文
1. The Hungarian director has completed her powerfl Diary trilogy ,set against the background of events in her country.