watcher

watcher
    n 1: 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" [syn: {spectator}, {witness},
         {viewer}, {watcher}, {looker}]
    2: a guard who keeps watch [syn: {watchman}, {watcher},
       {security guard}]
    3: a person who keeps a devotional vigil by a sick bed or by a
       dead body
    

Watcher \Watch"er\ (-[~e]r), n.
   One who watches; one who sits up or continues; a diligent
   observer; specifically, one who attends upon the sick during
   the night.
   [1913 Webster]
    

52 Moby Thesaurus words for "watcher":
      Argus, Charley, TV-viewer, airplane spotter, beholder,
      bird-watcher, bystander, drugstore cowboy, eyewitness,
      fire patrolman, fire warden, fireguard, forward observer, gaper,
      gazer, gazer-on, girl-watcher, goggler, kibitzer, looker,
      looker-on, lookout, lookout man, night watchman, observer, ogler,
      onlooker, patrol, patroller, patrolman, perceiver, percipient,
      picket, roundsman, scout, seer, sentinel, sentry,
      sidewalk superintendent, spectator, spectatress, spectatrix,
      spotter, televiewer, television-viewer, vedette, video-gazer,
      viewer, watch, watchkeeper, watchman, witness