obligational - n.
1 the constraining power of a law, precept, duty, contract, etc.
2 a duty; a burdensome task.
3 a binding agreement, esp. one enforceable under legal penalty; a written contract or bond.
4 a a service or benefit (repay an obligation). b indebtedness for this (be under an obligation).

day of obligation Eccl. a day on which all are required to attend Mass or Communion. of obligation obligatory.

obligational adj. [ME f. OF f. L obligatio -onis (as OBLIGE)]