noun (n)

• a close observer; someone who looks at something (such as an exhibition of some kind)(noun.person)

  Example:
  Sky watchers discovered a new star.
  

  Synonym:
  looker, spectator, viewer, witness
  

  source: wordnet30
• a guard who keeps watch(noun.person)

  Synonym:
  security guard, watchman
  

  source: wordnet30
• a person who keeps a devotional vigil by a sick bed or by a dead body(noun.person)

  source: wordnet30
• One who watches; one who sits up or continues; a diligent observer; specifically, one who attends upon the sick during the night.(noun)

  source: webster1913