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):

inadvertency
    n 1: the trait of forgetting or ignoring your responsibilities
         [syn: unmindfulness, heedlessness, inadvertence,
         inadvertency] [ant: heedfulness, mindfulness]