English to English

noun (n)

• someone who systematically obstructs some action that others want to take(noun.person)

  Synonym:
  obstructer, obstructionist, obstructor, thwarter
  

  source: wordnet30
• someone who offers opposition(noun.person)

  Synonym:
  adversary, antagonist, opponent, opposer
  Antonym:
  agonist
  

  source: wordnet30
• One who resists.(noun)

  source: webster1913