Source : Webster's Revised Unabridged Dictionary (1913)

Oversleep \O`ver*sleep"\, v. t.
   To sleep beyond; as, to oversleep one's self or one's usual
   hour of rising.

Oversleep \O`ver*sleep"\, v. i.
   To sleep too long.

Source : WordNet®

oversleep
     v : sleep longer than intended
     [also: {overslept}]