What is the Meaning of the Expression
ON DUTY?

Definition:

working at that time (at one’s job)

This is especially used for jobs where it is necessary for someone be available at all times, such as medical staff, fire fighters, police officers, etc.

Example:

He was on duty when the plane crashed. All the firefighters in the area were called to the scene.

 

Note:  This vocabulary is used in the online course below.

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