An onlooker is someone who watches something but isn't directly involved in it. The spectators at a boxing match or a dog show or a marathon are all onlookers.

If you observe an event but you don't participate in it, you're an onlooker. The event itself might be a performance of some kind, like a concert or a football match, or it might be some undesirable occurrence: "The firefighters battled the blaze while onlookers watched in horror." Onlooker dates from the early seventeenth century, from the sense of "looking on."

Definitions of onlooker

n someone who looks on

Type of:
looker, spectator, viewer, watcher, witness
a close observer; someone who looks at something (such as an exhibition of some kind)

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