tril·o·gy /ˈtrɪləʤi/
三部劇,三部曲
Tril·o·gy n. A series of three dramas which, although each of them is in one sense complete, have a close mutual relation, and form one historical and poetical picture. Shakespeare's “ Henry VI.” is an example.
On the Greek stage, a drama, or acted story, consisted in reality of three dramas, called together a trilogy, and performed consecutively in the course of one day. --Coleridge.
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trilogy
n : a set of three literary or dramatic works related in subject
or theme