Noun
(law) The charge or care of certain officers to keep a watch by night and a guard by day in towns, cities, and other districts, for the preservation of the public peace.
(by extension) Uninterrupted vigilance.
Source: en.wiktionary.orgWe are not here today to bow before the representation of a fierce warlike god, filled with wrath and vengeance, but we joyously contemplate instead our own deity keeping watch and ward before the open gates of America and greater than all that have been celebrated in ancient song. Grover Cleveland
Every citizen of the republic ought to consider himself an unofficial policeman, and keep unsalaried watch and ward over the laws and their execution. Mark Twain