English definition of “duty”
/ˈdjuːti/ noun [C, U]
RIGHT THING TO DO › something you must do because it is morally or legally right: a moral duty [+ to do sth] Rail companies have a duty to provide safe transport.
JOB › something you do as part of your job or because of your position: professional/official duties
on/off duty › If a doctor, police officer, etc is on duty, they are working, and if they are off duty, they are not working: I'm on duty tomorrow night.
TAX › tax that you pay on something you buy