The Collaborative International Dictionary of English v.0.48:

Neglect \Neg*lect"\, v. t. [imp. & p. p. Neglected; p. pr. &
   vb. n. Neglecting.] [L. neglectus, p. p. of neglegere
   (negligere) to disregard, neglect, the literal sense prob.
   being, not to pick up; nec not, nor (fr. ne not + -que, a
   particle akin to Goth. -h, -uh, and prob. to E. who; cf.
   Goth. nih nor) + L. legere to pick up, gather. See No,
   adv., Legend, Who.]
   1. Not to attend to with due care or attention; to forbear
      one's duty in regard to; to allow to pass unimproved,
      unheeded, undone, etc.; to omit; to disregard; to slight;
      as, to neglect duty or business; to neglect to pay debts.
      [1913 Webster]

            I hope
            My absence doth neglect no great designs. --Shak.
      [1913 Webster]

            This, my long suffering and my day of grace,
            Those who neglect and scorn shall never taste.
                                                  --Milton.
      [1913 Webster]

   2. To omit to notice; to forbear to treat with attention or
      respect; to slight; as, to neglect strangers.
      [1913 Webster]

   Syn: To slight; overlook; disregard; disesteem; contemn. See
        Slight.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Neglect \Neg*lect"\, n. [L. neglectus. See Neglect, v.]
   1. Omission of proper attention; avoidance or disregard of
      duty, from heedlessness, indifference, or willfulness;
      failure to do, use, or heed anything; culpable disregard;
      as, neglect of business, of health, of economy.
      [1913 Webster]

            To tell thee sadly, shepherd, without blame,
            Or our neglect, we lost her as we came. --Milton.
      [1913 Webster]

   2. Omission of attention or civilities; slight; as, neglect
      of strangers.
      [1913 Webster]

   3. Habitual carelessness; negligence.
      [1913 Webster]

            Age breeds neglect in all.            --Denham.
      [1913 Webster]

   4. The state of being disregarded, slighted, or neglected.
      [1913 Webster]

            Rescue my poor remains from vile neglect. --Prior.
      [1913 Webster]

   Syn: Negligence; inattention; disregard; disesteem;
        remissness; indifference. See Negligence.
        [1913 Webster]

   benign neglect A deliberate policy of minimizing public
      discussion of a controversial issue [e.g. by the
      president] on the theory that excessive discussion in
      itself is harmful or counterproductive.
      [PJC]

WordNet (r) 3.0 (2006):

neglect
    n 1: lack of attention and due care [syn: disregard,
         neglect]
    2: the state of something that has been unused and neglected;
       "the house was in a terrible state of neglect" [syn:
       neglect, disuse]
    3: willful lack of care and attention [syn: disregard,
       neglect]
    4: the trait of neglecting responsibilities and lacking concern
       [syn: negligence, neglect, neglectfulness]
    5: failure to act with the prudence that a reasonable person
       would exercise under the same circumstances [syn:
       negligence, carelessness, neglect, nonperformance]
    v 1: leave undone or leave out; "How could I miss that typo?";
         "The workers on the conveyor belt miss one out of ten"
         [syn: neglect, pretermit, omit, drop, miss,
         leave out, overlook, overleap] [ant: attend to,
         take to heart]
    2: fail to do something; leave something undone; "She failed to
       notice that her child was no longer in his crib"; "The
       secretary failed to call the customer and the company lost
       the account" [syn: fail, neglect]
    3: fail to attend to; "he neglects his children"
    4: give little or no attention to; "Disregard the errors" [syn:
       neglect, ignore, disregard]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "neglect":
   Sisyphean labor, abandon, bad policy, be caught napping,
   be neglectful, be negligent, blink at, brush off, carelessness,
   cold-shoulder, contemn, cut, cut dead, default, delinquency,
   dereliction, disconformity, discount, disdain, dismiss, disregard,
   disrespect, elide, endless task, fail, failing, failure, forget,
   give the go-by, gloss over, heedlessness, ignore, impolicy,
   inaction, inactivity, inadvertence, inattention, indifference,
   inexecution, inexpedience, inexpediency, inobservance, lapse,
   laxity, laxness, leave undone, let go, let pass, let ride,
   let slide, let slip, look right through, loose ends, lose sight of,
   lose track of, make little of, maladministration, malfeasance,
   malpractice, misadministration, misconduct, misdirection,
   misfeasance, misgovernment, misguidance, mishandling,
   mismanagement, misrule, miss, neglectfulness, negligence, nod,
   nonaccomplishment, nonachievement, nonadherence, noncompliance,
   nonconformance, nonconformity, nonconsummation, nondischarging,
   nonexecution, nonfeasance, nonfulfillment, nonobservance,
   nonperformance, not care for, not get involved, not heed,
   not think, omission, omit, overleap, overlook, overpass, oversight,
   pass, pass by, pass over, pass up, passiveness, passivity,
   pooh-pooh, pretermit, rebuff, refuse to acknowledge,
   refuse to recognize, reject, remissness, rough edges, scant, scorn,
   shirk, shrug off, slackness, sleep, slight, slighting, slur over,
   spurn, take for granted, think little of, unconcern, unfulfillment,
   unobservance, work of Penelope, wrongdoing