Source : Webster's Revised Unabridged Dictionary (1913)

Sisyphus \Sis"y*phus\, n. [L. Sisyphus, Sisyphus, fr. Gr. ????.]
   (Class. Myth.)
   A king of Corinth, son of [AE]olus, famed for his cunning. He
   was killed by Theseus, and in the lower world was condemned
   by Pluto to roll to the top of a hill a huge stone, which
   constantly rolled back again, making his task incessant.

Source : WordNet®

Sisyphus
     n : (Greek legend) a king in ancient Greece who offended Zeus
         and whose punishment was to roll a huge boulder to the
         top of a steep hill; each time the boulder neared the top
         it rolled back down and Sisyphus was forced to start
         again