Tra từ observer - Từ điển Oxford Advanced Learner 8th

ob·ser·ver [observer observers] BrE [əbˈzɜːvə(r)] NAmE [əbˈzɜːrvər] noun
1. a person who watches sb/sth
•According to observers, the plane exploded shortly after take-off.
•To the casual observer (= somebody who does not pay much attention), the system appears confusing.
•Most art forms require a contribution from the observer.
2. a person who attends a meeting, lesson, etc. to listen and watch but not to take part
•A team of British officials were sent as observers to the conference.
3. a person who watches and studies particular events, situations, etc. and is therefore considered to be an expert on them
•a royal observer

Word Origin:
mid 16th cent.: from ↑observe + ↑-er.

Synonyms:
witness
observer • onlooker • passer-by • bystander • eyewitness
These are all words for a person who sees sth happen.
witness • a person who sees sth happen and is able to describe it to other people; a person who gives evidence in a court of law: ▪ Police have appealed for ▪ witnesses to ▪ the accident.
observer • a person who sees sth happen: ▪ According to observers, the plane exploded shortly after take-off.
onlooker • a person who watches sth that is happening but is not involved in it: ▪ A crowd of onlookers gathered at the scene of the crash.
passer-by • a person who is going past sb/sth by chance, especially when sth unexpected happens: ▪ Police asked passers-by if they had witnessed the accident.
bystander • a person who is near and can see what is happening when sth such as an accident or fight takes place: ▪ Three ▪ innocent bystanders ▪ were killed in the crossfire.
eyewitness • a person who has seen a crime or accident and can describe it afterwards.
a(n) witness/observer/onlooker/passer-by/bystander/an eyewitness sees sth
a(n) observer/onlooker/passer-by/bystander witnesses sth

Example Bank:
•I attended the conference as an observer.
•Independent observers will monitor the elections.
•Observers were sent to check the conduct of the elections.
•Some military observers fear the US could get entangled in another war.
•The country was granted observer status at the summit.
•The suddenness of this move surprised many observers.
•The talks were attended by observers from eight Arab countries and Israel.
•To the casual observer, it would have looked like any other domestic argument.
•an observer of the American cultural scene
•Observers noted an absence of the violence which had been a feature of previous elections.
•To Western observers, their political system is strikingly different.