onlooker

Từ điển Oxford Advanced Learner 8th

on·look·er [onlooker onlookers] BrE [ˈɒnlʊkə(r)] NAmE [ˈɑːnlʊkər] NAmE [ˈɔːnlʊkər] noun
a person who watches sth that is happening but is not involved in it
Syn: ↑bystander
•A crowd of onlookers gathered at the scene of the crash.

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