police. To watch is, properly speaking, to stand sentry and attend guard during the night time: certain officers called watchmen are appointed in most of the United States, whose duty it is to arrest all persons who are violating the law, or breaking the peace.
Law Dictionary – Alternative Legal Definition
(noun) – A body of constables on duty on any particular night.
(verb) – To keep guard; to stand as sentinel; to be on guard at night, for the preservation of the peace and good order.