The chief magistrate of a city, elected by the citizens, and holding office for twelve months. The chief magistrate of London is The Right Hon. the Lord Mayor, one of the Privy Council.
Since 1389 the chief magistrate of York has been a Lord Mayor, and in 1894 those of Liverpool and Manchester.
There are two Lord Mayors of Ireland, viz. those of Dublin (1685) and of Belfast; and four of Scotland- Glasgow, Edinburgh, Aberdeen, and Dundee.
At the Conquest the sovereign appointed the chief magistrates of cities. That of London was called the
Port-Reeve, but Henry II. changed the word to the Norman maire (our mayor). John made the office annual; and Edward III. (in 1354) conferred the title of “The Right Hon. the Lord Mayor of London.”
The first Lord Mayor's Show was 1458, when Sir John Norman went by water in state, to be sworn in at Westminster; and the cap and sword were given by Richard II. to Sir William Walworth, for killing Wat Tyler.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894