Often in a context of careful observation; the watch a watchman or group of watchmen who patrolled and guarded the streets of a town before the introduction of the police force.
watch and ward the performance of the duty of a watchman or sentinel, especially as a feudal obligation. It has traditionally been suggested that watch referred to service by night and ward to service by day, but there is no evidence for this as an original meaning.
The Watch on the Rhine a German patriotic song, Die Wacht am Rhein (1840), written by Max Schneckenburger, which was set to music by Karl Wilhelm in 1854, and became a popular Prussian soldiers' song in the Franco-Prussian War.
watch the world go by spend time observing other people going about their business.
See also watch someone like a hawk, like watching paint dry, watch someone's smoke, watched, watches.