observer
n
1 person who observes 观察者; 遵守者; 评论者
an observer of nature 自然界的观察家
a poor observer of speed restrictions 不遵守速度限制的人.
2 person who attends a conference, lesson, etc to listen and watch but not to take part （会议、 课堂等的）观察员, 旁听者
an observer at a summit conference 高峰会议上的观察员
send sb along as an observer 派某人作观察员.