Bangor: clock tower plaque

The plaque, on the side of the SH5872 : Bangor: the clock tower, explains that it was: "Erected and presented to the city of Bangor by Alderman Thomas Lewis, JP, Garth'erwen, during his mayoralty, as a token of his interest in the welfare of the city. 1886-7" Any explanations of what "Garth'erwen" means?