a person who watches something that is happening but is not involved in itsynonymbystanderA crowd of onlookers gathered at the scene of the crash.Synonymswitnessobserveronlookerpasser-bybystandereyewitnessThese are all words for a person who sees something happen.witness a person who sees something 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 something happen:According to observers, the plane exploded shortly after take-off.onlooker a person who watches something 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 somebody/something by chance, especially when something 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 something 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.Patterns a witness/an observer/an onlooker/a passer-by/a bystander/an eyewitness sees something an observer/an onlooker/a passer-by/a bystander witnesses something
See onlooker in the Oxford Advanced American Dictionary
