Meaning of “guard” - Learner’s Dictionary

guard

noun uk us /ɡɑːd/
PROTECT [ C ]

B1 someone whose job is to make certain someone does not escape or to protect a place or another person:

a security guard
prison guards
SOLDIERS [ no plural ]
TRAIN [ C ] (also conductor)

someone who is in charge of a train

THING [ C ]

something that covers or protects someone or something:

a fire guard
be on guard; stand guard

to be responsible for protecting a place or a person:

Armed police stood guard outside the house.
be under guard

to be kept in a place by a group of people who have weapons:

The suspect is now under guard in the local hospital.

(Definition of “guard noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)