ETYM From Due.
1. The social force that binds one to one's obligations and the courses of action demanded by that force.
2. Work that one is obliged to perform for moral or legal reasons.
Moral obligation experienced as a felt commandment of the moral law. Moral conflicts occur where a number of duties make apparently irreconcilable demands on us.
The stoics in ancient Greece and Immanuel Kant in Germany (who coined the concept of the categorical imperative) are the moral philosophers who have placed greatest emphasis on duty. Duty is strongly emphasized in Confucianism (especially duty to the state and to ancestors) and in Japanese culture, where it is divided into obligations (on) that can and therefore must be repaid, and continuous obligations, such as those to parents and country.

A tax on a good. A customs duty is a tax on goods entering a country (a tax on imports). An excise duty is a type of indirect tax on goods consumed such as gasoline, alcohol, or tobacco.
A government tax on imports or exports; SYN. tariff.