Source : Webster's Revised Unabridged Dictionary (1913)

Obolus \Ob"o*lus\, n.;pl. {Oboli}. [L., fr Gr. (?)] (Gr.Antiq.)
   (a) A small silver coin of Athens, the sixth part of a
       drachma, about three cents in value.
   (b) An ancient weight, the sixth part of a drachm.

Source : WordNet®

obolus
     n : a Greek unit of weight equal to one tenth of a gram
     [also: {oboli} (pl)]