obligation

noun

1. (countable, uncountable)The act of binding oneself by a social, legal, or moral tie to someone.
2. (countable, uncountable)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. (countable, uncountable)A course of action imposed by society, law, or conscience by which someone is bound or restricted.
4. (countable, uncountable)A legal agreement stipulating a specified action or forbearance by a party to the agreement; the document containing such agreement.

   “The Pupil after his Pupillarity, had granted a Diſcharge to one of the Co-tutors, which did extinguiſh the whole Debt of that Co-tutor, and conſequently of all the reſt, they being all correi debendi, lyable by one individual Obligation, which cannot be Diſcharged as to one, and ſtand as to all the reſt.”

5. (countable)Reason for being obliged to, that is, grateful for, something.

   “I am indebted to several friends for notes, observations, and correspondence on this subject, more especially to one, referred to as "Z.," and to another as "Q.," who have obtained a considerable number of reliable histories for me, and have also supplied many valuable notes [...]. Other obligations are mentioned in the text.”