An onlooker is someone who watches an event take place but does not take part in it.
例句
A handful of onlookers stand in the field watching.少數幾個旁觀者站在現場觀看。
英漢詞典釋義
n.
旁觀者, 觀看者
She blew a kiss to the onlookers.她向旁觀的人群送去一個飛吻。A crowd of onlookers formed around the fight.旁觀者聚集起來圍觀斗毆。After the crash,onlookers said that the plane had suddenly dropped down out of the sky.飛機墜毀后旁觀者說飛機是突然從天上掉下來的。