Noun
Lord High Steward (plural Lord High Stewards)
The first of the Great Officers of State in England, nominally ranking above the Lord Chancellor. The office has generally remained vacant since 1421 and is now primarily ceremonial and filled only for a coronation.
If Parliament is not in session, then the trial is conducted by a "Court of the Lord High Steward" instead of the House of Lords (even if the defendant is not a peer). Source: Internet
The procedure used to be that the Lord Chancellor presided (or the Lord High Steward if the defendant was a peer ); but this was when the Lord Chancellor was both the Lords' presiding officer and head of the judiciary of England and Wales. Source: Internet