observer
/əbˈzɜːvə(r)/noun
1- a person who watches or notices something观察者：
to a casual observer, he was at peace.
对一个随意的观察者来说, 他很平静。
1.1
- a person who follows events, especially political ones, closely and comments publicly on them（尤指政治事件的）观察家：
some observers expect interest rates to rise.
一些观察家预计利率会上升。
1.2
- a person posted in an official capacity to an area to monitor political or military events（专职监督政治或军事事件的）观察员：
elections scrutinized by international observers.
由国际观察员监督的选举。
1.3
- a person who attends a conference, inquiry, etc., to note the proceedings without participating in them（出席会议、调查等但不参与其中的）观察员。
1.4
- (in science or art) a real or hypothetical observer regarded as having a particular viewpoint or effect（科学或艺术中被认为持有某种观点或能产生某种影响的真实或假想的）观察者。
1.5
- a person trained to spot and identify enemy aircraft or to reconnoitre enemy positions from the air（发现和识别敌机的）观察员; （从空中侦察敌方阵地的）空中观察员。