obligation

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act of binding oneself by a social, legal, or moral tie.
2. n. A social, legal, or moral requirement, such as a duty, contract, or promise that compels one to follow or avoid a particular course of action.
3. n. A course of action imposed by society, law, or conscience by which one is bound or restricted.
4. n. The constraining power of a promise, contract, law, or sense of duty.
5. n. Law A legal agreement stipulating a specified payment or action, especially if the agreement also specifies a penalty for failure to comply.
6. n. Law The document containing the terms of such an agreement.
7. n. Something owed as payment or in return for a special service or favor.
8. n. The service or favor for which one is indebted to another.
9. n. The state, fact, or feeling of being indebted to another for a special service or favor received.

Century Dictionary and Cyclopedia

1. n. The constraining power or authoritative character of a duty, a moral precept, a civil law, or a promise or contract voluntarily made; action upon the will by a sense of moral constraint.
2. n. That to which one is bound; that which one is bound or obliged to do, especially by moral or legal claims; a duty.
3. n. A claim; a ground of demanding.
4. n. The state or fact of being bound or morally constrained by gratitude to requite benefits; moral indebtedness.
5. n. In law: A bond containing a penalty, with a condition annexed, for payment of money, performance of covenants, or the like: sometimes styled a writing obligatory. By some modern English jurists the word is used as equivalent to legal duty generally.
6. n. In Roman law, the juridical relation between two or more persons in virtue of which one can compel the other to do or not to do a certain act which has a monetary value, or can at least be measured by a monetary standard. It might arise out of delict as well as out of contract. The word is used as well to designate the right as the corresponding duty.
7. n. In medieval schools, a rule of disputation by which the opponent was bound to admit any premise, not involving a contradiction, begging of the question, or other fallacy, which the respondent might propose. Disputation, as a game for teaching logic, was a principal part of the scholastic exercises, and perhaps may still be so in some countries. A master presided, and after a sufficient time decided in favor of one of the disputants, who was then obliged to give his adversary a great thwack with a wooden instrument. Modern writers sometimes speak of any rule of scholastic disputation as an obligation.
8. n. Synonyms Engagement, contract, agreement.

Wiktionary

1. n. The act of binding oneself by a social, legal, or moral tie to someone.
2. n. A social, legal, or moral requirement, duty, contract, or promise that compels someone to follow or avoid a particular course of action.
3. n. A course of action imposed by society, law, or conscience by which someone is bound or restricted.
4. n. law A legal agreement stipulating a specified payment or action; the document containing such agreement.

GNU Webster's 1913

1. n. The act of obligating.
2. n. That which obligates or constrains; the binding power of a promise, contract, oath, or vow, or of law; that which constitutes legal or moral duty.
3. n. Any act by which a person becomes bound to do something to or for another, or to forbear something; external duties imposed by law, promise, or contract, by the relations of society, or by courtesy, kindness, etc.
4. n. The state of being obligated or bound; the state of being indebted for an act of favor or kindness; -- often used with under to indicate being in that state.
5. n. (Law) A bond with a condition annexed, and a penalty for nonfulfillment. In a larger sense, it is an acknowledgment of a duty to pay a certain sum or do a certain things.

WordNet 3.0

1. n. a personal relation in which one is indebted for a service or favor
2. n. the social force that binds you to the courses of action demanded by that force
3. n. a written promise to repay a debt
4. n. a legal agreement specifying a payment or action and the penalty for failure to comply
5. n. the state of being obligated to do or pay something