Idioms
a/your bounden ˈduty
(old-fashioned, formal) something that you feel you must do; a responsibility which cannot be ignored
He felt it was his bounden duty to tell the police what he knew.
We have a bounden duty to respond to this call for help.
in the ˌline of ˈduty
while doing a job
A policeman was injured in the line of duty yesterday.
on/off duty
(of nurses, police officers, etc.) working/not working at a particular time
Who's on duty today?
What time do you go off duty?
see also off-duty