The Great Key of Rassilon

The Great Key is sometimes used to refer to the Rod of Rassilon

The Great Key (also known as the Great Key of Rassilon) was one of the Artefacts of Rassilon, which was never (except in rare circumstances) in possession of the Lord President, the Chancellor typically held the Great Key. A forbidden weapon known as the De-mat Gun was activated by the Great Key. (DW: The Invasion of Time)