noun (n)

• someone who comes upon something after searching(noun.person)

  source: wordnet30
• someone who is the first to observe something(noun.person)

  Synonym:
  discoverer, spotter
  

  source: wordnet30
• optical device that helps a user to find the target of interest(noun.artifact)

  Synonym:
  view finder, viewfinder
  

  source: wordnet30
• One who, or that which, finds; specifically (Astron.), a small telescope of low power and large field of view, attached to a larger telescope, for the purpose of finding an object more readily.(noun)

  source: webster1913
• A slide ruled in squares, so as to assist in locating particular points in the field of vision.(noun)

  source: webster1913