noun (n)

• additional proof that something that was believed (some fact or hypothesis or theory) is correct(noun.cognition)

  Synonym:
  check, confirmation, verification
  

  source: wordnet30
• the act of validating; finding or testing the truth of something(noun.act)

  Synonym:
  proof, validation
  

  source: wordnet30
• The act of substantiating or proving; evidence; proof.(noun)

  source: webster1913