Duty (noun)

1. A moral or legal obligation; a responsibility.
2. A task or action that is required or expected as part of a job or role.

Origin:

From the old french "deu", meaning "owed" or "bound by a debt".

Examples:

1. It is your duty to obey the laws.
2. It is a parent's duty to take care of their children.
3. He is performing his duty as a police officer.
4. It is the duty of the government to protect its citizens.
5. I have to do my duty and vote in the election.