watcher

noun

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

   noun.person

   Examples

   Sky watchers discovered a new star.

   Synonyms looker spectator viewer witness

   Source: WordNet 3.0

2. a guard who keeps watch

   noun.person

   Synonyms security guard watchman

   Source: WordNet 3.0

3. a person who keeps a devotional vigil by a sick bed or by a dead body

   noun.person

   Source: WordNet 3.0

4. 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