Grand Secretary of the Grand Secretariat
Historical title for a high-ranking official in the imperial court of ancient China, specifically a member of the Grand Secretariat (内閣). Not used in modern Japanese contexts.
See also: 大学士
The Grand Secretaries of the Ming dynasty played an important role as close advisors to the emperor.
大学士 is a broader term for a high-ranking scholar-official in ancient China, while 内閣大学士 specifically denotes a Grand Secretary serving in the Grand Secretariat.
From Chinese 內閣大學士 (nèigé dàxuéshì), a title used in imperial China for senior officials of the Grand Secretariat. The Japanese reading is on'yomi.