(n.) One who watches; one who sits up or continues; a diligent observer; specifically, one who attends upon the sick during the night.

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