Source : Webster's Revised Unabridged Dictionary (1913)

Duty \Du"ty\, n.; pl. {Duties}. [From {Due}.]
   1. That which is due; payment. [Obs. as signifying a material
      thing.]

            When thou receivest money for thy labor or ware,
            thou receivest thy duty.              --Tyndale.

Source : WordNet®

duty
     n 1: work that you are obliged to perform for moral or legal
          reasons; "the duties of the job"
     2: the social force that binds you to your obligations and 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 [syn: {responsibility},
         {obligation}]
     3: a government tax on imports or exports; "they signed a
        treaty to lower duties on trade between their countries"
        [syn: {tariff}]