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.
   [1913 Webster]

   2. An act or instance of negligence or carelessness.
      [1913 Webster]

            remarking his beauties, . . . I must also point out
            his negligences and defects.          --Blair.
      [1913 Webster]

   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.
      [1913 Webster]

   Contributory negligence. See under Contributory.
      [1913 Webster]

   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]

Moby Thesaurus II by Grady Ward, 1.0:

170 Moby Thesaurus words for "negligence":
   absentmindedness, accidia, acedia, allowance, apathy,
   approximation, ataraxia, ataraxy, bad policy, blowziness,
   carelessness, casualness, chintziness, culpa, culpable negligence,
   default, delinquency, dereliction, detachment, deviation,
   disconformity, disinterest, dispassion, disregard,
   disregardfulness, distraction, dowdiness, easiness, easygoingness,
   failing, failure, fecklessness, flightiness, flippancy,
   forgetfulness, frivolousness, frowziness, frumpishness, giddiness,
   grubbiness, hastiness, heedlessness, impolicy, impotence,
   imprecision, improvidence, inaccuracy, inaccurateness,
   inadvertence, inadvertency, inattention, inattentiveness,
   inconsideration, incorrectness, incuriosity, indifference,
   indiscrimination, inexactitude, inexactness, inexcitability,
   inexpedience, inexpediency, inobservance, insouciance, laches,
   lack of affect, lackadaisicalness, laissez-faire, lapse,
   lax stewardship, laxity, laxness, leniency, levity,
   lightmindedness, listlessness, looseness, loosening,
   maladministration, malfeasance, malpractice, messiness,
   mindlessness, misadministration, misconduct, misdirection,
   misfeasance, misgovernment, misguidance, mishandling,
   mismanagement, misrule, neglect, neglectfulness, nonadherence,
   nonchalance, noncompliance, nonconformance, nonconformity,
   nonfeasance, nonfulfillment, noninterference, nonobservance,
   nonperformance, nonrestriction, obliviousness, omission, oscitancy,
   overindulgence, overlooking, overpermissiveness, oversight,
   permissiveness, pococurantism, poor husbandry, poor stewardship,
   predictable error, probable error, procrastination, recklessness,
   regardlessness, relaxation, relaxedness, remissness, seediness,
   shabbiness, shallowness, shiftlessness, shoddiness, slackness,
   slatternliness, slight, slipshodness, sloppiness, sloth,
   slovenliness, slovenry, sluttishness, softness, sordidness,
   squalidness, squalor, standard deviation, superficiality,
   tackiness, tawdriness, thoughtlessness, thriftlessness, tolerance,
   unalertness, unanxiousness, unawareness, unconcern,
   unconsciousness, uncorrectness, unfactualness, unheedfulness,
   unintentiveness, unmindfulness, unneatness, unobservance,
   unpreciseness, unrestraint, unrigorousness, unsolicitousness,
   untidiness, unwariness, unwatchfulness, weakness, wrongdoing