He owns an 18th-century rare-book that is worth a fortune.

rare-book 是由形容词 rare（稀有的、珍贵的）和名词 book（书）组成的复合词，中间用连字符连接。rare-book 指"珍本、稀有书籍"，特指那些存世稀少、具有收藏价值的书籍。