The Collaborative International Dictionary of English v.0.48:

Overwork \O`ver*work"\, v. t. [imp. & p. p. Overworkedor
   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.
      [1913 Webster]

   2. To fill too full of work; to crowd with labor.
      [1913 Webster]

            My days with toil are overwrought.    --Longfellow.
      [1913 Webster]

   3. To decorate all over.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overwork \O`ver*work"\, v. i.
   To work too much, or beyond one's strength.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overwork \O"ver*work`\, n.
   Work in excess of the usual or stipulated time or quantity;
   extra work; also, excessive labor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

The Devil's Dictionary (1881-1906):

OVERWORK, n.  A dangerous disorder affecting high public functionaries
who want to go fishing.