The Collaborative International Dictionary of English v.0.48:

Inadvertence \In`ad*vert"ence\; pl. -ces, Inadvertency
\In`ad*vert"en*cy\; pl. -cies, n. [Cf. F. inadvertance.]
   [1913 Webster]
   1. The quality of being inadvertent; lack of heedfulness or
      attentiveness; inattention; negligence; as, many mistakes
      proceed from inadvertence.
      [1913 Webster]

            Inadvertency, or lack of attendance to the sense and
            intention of our prayers.             --Jer. Taylor.
      [1913 Webster]

   2. An effect of inattention; a result of carelessness; an
      oversight, mistake, or fault from negligence.
      [1913 Webster]

            The productions of a great genius, with many lapses
            an inadvertencies, are infinitely preferable to
            works of an inferior kind of author which are
            scrupulously exact.                   --Addison.

   Syn: Inattention; heedlessness; carelessness; negligence;
        thoughtlessness. See Inattention.
        [1913 Webster]

WordNet (r) 3.0 (2006):

inadvertence
    n 1: an unintentional omission resulting from failure to notice
         something [syn: oversight, inadvertence]
    2: the trait of forgetting or ignoring your responsibilities
       [syn: unmindfulness, heedlessness, inadvertence,
       inadvertency] [ant: heedfulness, mindfulness]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "inadvertence":
   absentmindedness, balk, bevue, carelessness, culpa,
   culpable negligence, default, dereliction, disregard,
   disregardfulness, distraction, failure, false move, false step,
   flightiness, flippancy, frivolousness, giddiness, heedlessness,
   inadvertency, inattention, inattentiveness, inconsideration,
   incuriosity, indifference, inobservance, laches, laissez-faire,
   lapse, lapsus calami, lapsus linguae, laxity, laxness, levity,
   lightmindedness, loose thread, looseness, miscue, misstep, neglect,
   neglectfulness, negligence, nonfeasance, noninterference,
   nonobservance, nonperformance, nonrestriction, obliviousness,
   omission, overlooking, oversight, permissiveness, poor stewardship,
   procrastination, regardlessness, remissness, shallowness,
   slackness, slight, slip, slipup, stumble, superficiality,
   thoughtlessness, trip, unalertness, unawareness, unconsciousness,
   unheedfulness, unintentiveness, unmindfulness, unobservance,
   unrigorousness, unwariness, unwatchfulness, wrong step