Source : Webster's Revised Unabridged Dictionary (1913)

Overwork \O`ver*work"\, v. t. [imp. & p. p. {Overworked}or
   {Overwrought}; p. pr. & vb. n. {Overworking}.]
   1. To work beyond the strength; to cause to labor too much or
      too long; to tire excessively; as, to overwork a horse.

   2. To fill too full of work; to crowd with labor.

            My days with toil are overwrought.    --Longfellow.

   3. To decorate all over.

Overwork \O`ver*work"\, v. t.
   To work too much, or beyond one's strength.

Overwork \O"ver*work`\, n.
   Work in excess of the usual or stipulated time or quantity;
   extra work; also, excessive labor.

Source : WordNet®

overwork
     n : the act working too much or too long; "he became ill from
         overwork" [syn: {overworking}]
     v 1: use too much; "This play has been overworked"
     2: work excessively hard; "he is exploiting the students" [syn:
         {exploit}]