onlooker
1 synonym for onlooker, grouped by meaning and by how common each one is.
Noun — A person who watches something happen without joining in.
Synonyms
Rare, literary or technical
Precise, but they will stand out — check the sense before using one.
Etymology
From on + look + -er, probably from the verb look on, but compare with onlook.
Full origin of onlooker →