adjective (a)

• characterized by neglect and undue lack of concern(adj.all)

  Example:
  Negligent parents.
  Negligent of detail.
  Negligent in his correspondence.
  

  Antonym:
  diligent
  

  source: wordnet30
• Apt to neglect; customarily neglectful; characterized by negligence; careless; heedless; culpably careless; showing lack of attention; as, disposed in negligent order.(adjective)

  source: webster1913