obligation in WordNet English dictionary

1. a written promise to repay a debt
   debt instrument  obligation  certificate of indebtedness 
   
2. the social force that binds you to the courses of action demanded by that force
   "we must instill a sense of duty in our children"; "every right implies a responsibility; every opportunity, an obligation; every possession, a duty"- John D.Rockefeller Jr
   duty  responsibility  obligation 
   
3. a personal relation in which one is indebted for a service or favor
   obligation  indebtedness 
   
4. a legal agreement specifying a payment or action and the penalty for failure to comply
   obligation 
   
5. the state of being obligated to do or pay something
   "he is under an obligation to finish the job"
   obligation