noun (n)

• a mistake resulting from neglect(noun.act)

  Synonym:
  skip
  

  source: wordnet30
• something that has been omitted(noun.state)

  Example:
  She searched the table for omissions.
  

  source: wordnet30
• any process whereby sounds or words are left out of spoken words or phrases(noun.process)

  Synonym:
  deletion
  

  source: wordnet30
• neglecting to do something; leaving out or passing over something(noun.cognition)

  source: wordnet30
• The act of omitting; neglect or failure to do something required by propriety or duty.(noun)

  source: webster1913