Obligation

Noun

1. The act of binding oneself by a social, legal, or moral tie to someone.
2. A social, legal, or moral requirement, duty, contract, or promise that compels someone to follow or avoid a particular course of action.

   "I feel I'm under obligation to attend my sister's wedding, even though we have a very frosty relationship."

3. A course of action imposed by society, law, or conscience by which someone is bound or restricted.
4. A legal agreement stipulating a specified action or forbearance by a party to the agreement; the document containing such agreement.
5. Reason for being obliged to, that is, grateful for, something.