The Collaborative International Dictionary of English v.0.48:

Negligence \Neg"li*gence\, n. [F. n['e]gligence, L.
   negligentia.]
   The quality or state of being negligent; lack of due
   diligence or care; omission of duty; habitual neglect;
   heedlessness.
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   2. An act or instance of negligence or carelessness.
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            remarking his beauties, . . . I must also point out
            his negligences and defects.          --Blair.
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   3. (Law) The omission of the care usual under the
      circumstances, being convertible with the Roman culpa. A
      specialist is bound to higher skill and diligence in his
      specialty than one who is not a specialist, and liability
      for negligence varies acordingly.
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   Contributory negligence. See under Contributory.
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   Syn: Neglect; inattention; heedlessness; disregard; slight.

   Usage: Negligence, Neglect. These two words are freely
          interchanged in our older writers; but a distinction
          has gradually sprung up between them. As now generally
          used, negligence is the habit, and neglect the act, of
          leaving things undone or unattended to. We are
          negligent as a general trait of character; we are
          guilty of neglect in particular cases, or in reference
          to individuals who had a right to our attentions.
          [1913 Webster]

WordNet (r) 3.0 (2006):

negligence
    n 1: failure to act with the prudence that a reasonable person
         would exercise under the same circumstances [syn:
         negligence, carelessness, neglect, nonperformance]
    2: the trait of neglecting responsibilities and lacking concern
       [syn: negligence, neglect, neglectfulness]