An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Something by which a person is bound or obliged to do certain things, and which arises out of a sense of duty or results from custom, law, etc.
2) Something that is done or is to be done for such reasons (Dictionary.com).

M.E. obligacioun, from O.Fr. obligacion "obligation, duty, responsibility," from L. obligationem "an engaging or pledging," literally "a binding," noun of action from p.p. stem of obligare "to bind, bind up, bandage," from → ob- "to" + ligare "to bind," from PIE root *leig- "to bind."

Fariz, from Mid.Pers. frêz "obligation; duty."