Definition of bystander noun from the Oxford Advanced Learner's Dictionary

 

bystander

 noun
noun
BrE BrE//ˈbaɪstændə(r)//
 
; NAmE NAmE//ˈbaɪstændər//
 
 
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a person who sees something that is happening but is not involved synonym onlooker innocent bystanders at the scene of the accident Three innocent bystanders were killed in the crossfire. Synonymswitnessobserver onlooker passer-by bystander eyewitnessThese 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 the Oxford Advanced American Dictionary entry: bystander