Meaning of “duty” - Learner’s Dictionary

duty

noun [ C, U ] uk us /ˈdjuːti/
RIGHT THING TO DO

B1 something you must do because it is morally or legally right:

a moral duty
JOB

B2 something you do as part of your job or because of your position:

on/off duty

B2 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

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