guard:
(plural: ‘guards‘; pronunciation: the letter ‘g’ in this word rhymes with the letter ‘g’ in the word “garden”; and the letter ‘u’ has the same sound as ‘a’ in “garden”)

two security guards on duty
a person, especially a soldier, policeman, prison officer, watchman, security, whose job is to keep watch on somebody or something, such as a person, building, place, etc., and be in readiness to protect, defend or to stop somebody from doing something bad or against the rules or law;
a railway employee (official) in charge of a train [in American English – conductor];
a person or a group of people who form an escort to an important person or to show respect to a state/government official or politician,

a railway guard waving on duty
Our school security guard is so sincere on duty that even the principal cannot move about the school premises without being questioned!
There are several kinds of guards: a bodyguard who looks after the personal safety of important people; a security guard, also called ‘security officer’ or just ‘security’, who keeps law and order and provide safety for the people on a premises, such as malls, offices, large private homes, apartment buildings; a railway guard is an employee on a train who looks after the smooth journey of the train; a jail/prison guard who takes care of the inmates in a jail/prison; a member of a Coast Guard which is a military unit that keeps watch on the coasts of a country, preventing smugglers, illegal immigrants or enemies from entering the country from sea; a palace or castle guard is a member of a group of trained soldiers that guards a palace, castle or mansion and the royal family that lives in it; and a member of a National Guard, a unit of soldiers that comes into action during a national calamity or disaster or unrest in any large region to protect the people from anti-social elements.
Unfortunately, some unethical guards who are paid to protect people and property sometimes join hands with thieves and steal valuables from the premises they are supposed to be guarding, often causing injury or even death to the occupants.
