watcher

(n) a close observer; someone who looks at something (such as an exhibition of some kind)
- the spectators applauded the performance
- television viewers
- sky watchers discovered a new star
looker, spectator, viewer, witness,
(n) a guard who keeps watch security guard, watchman,
(n) a person who keeps a devotional vigil by a sick bed or by a dead body

looker spectator viewer witness security guard watchman