Synonyms witness
witness
observer ▪ onlooker ▪ passer-by ▪ bystander ▪ eyewitness
These 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