watchman
n.a person whose job is to guard a building or property, especially at night. They make sure the place is safe and that no one enters without permission.
n.a person employed to guard a building or property against intruders, fire, or damage. Often used in a historical or literary context, as 'security guard' is the more common modern equivalent.
“The watchman walks around the factory every hour at night.”
“The night watchman noticed the broken window and immediately called the police to report a break-in.”
“In the quiet hours before dawn, the lone watchman found solace in the rhythmic sound of his own footsteps echoing through the empty warehouse corridors.”
The plural form is 'watchmen'.
From Middle English waccheman. By surface analysis, watch + -man.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.