The Collaborative International Dictionary of English v.0.48:

Oversight \O"ver*sight`\, n.
   1. Watchful care; superintendence; general supervision.
      [1913 Webster]

   2. An overlooking; an omission; an error. --Hooker.
      [1913 Webster]

   3. Escape from an overlooked peril. [R.] "His fool-happy
      oversight." --Spenser.
      [1913 Webster]

   Syn: Superintendence; supervision; inspection; overlooking;
        inadvertence; neglect; mistake; error; omission.
        [1913 Webster]

WordNet (r) 3.0 (2006):

oversight
    n 1: an unintentional omission resulting from failure to notice
         something [syn: oversight, inadvertence]
    2: management by overseeing the performance or operation of a
       person or group [syn: supervision, supervising,
       superintendence, oversight]
    3: a mistake resulting from inattention [syn: oversight,
       lapse]