noun (n)

• a disloyal person who betrays or deserts his cause or religion or political party or friend etc.(noun.person)

  Synonym:
  apostate, ratter, recreant, renegade, turncoat
  

  source: wordnet30
• a person who abandons their duty (as on a military post)(noun.person)

  Synonym:
  defector
  

  source: wordnet30
• One who forsakes a duty, a cause or a party, a friend, or any one to whom he owes service; especially, a soldier or a seaman who abandons the service without leave; one guilty of desertion.(noun)

  source: webster1913