1 : conduct due to parents and superiors : respect
2 a : obligatory tasks, conduct, service, or functions that arise from one’s position (as in life or in a group) b (1) : assigned service or business (2) : active military service (3) : a period of being on duty
3 a : a moral or legal obligation b : the force of moral obligation
4 : tax; especially : a tax on imports
5 a : work 1a b (1) : the service required (as of an electric machine) under specified conditions (2) : functional application : use <got double duty out of the trip> (3) : use as a substitute <making the word do duty for the thing — Edward Sapir>

Etymology: Middle English duete, from Anglo-French deueté, dueté, from deu due

Date: 13th century

Duty (businessdictionary.com)

1. Ethical, legal, or moral accountability, owed always or for a certain period, specially to someone who has a corresponding right to demand satisfaction of an obligation.

2. Responsibility of conduct, function, or performance that arises from an express or implied contract, or from the fact of holding an office or position.

3. Alternative term for customs duty. See also duty of care and duty to act.