passer
n. countablen. a person who is walking past a specific place. You often use this to describe someone who happens to be nearby when something occurs.
n. a person who moves past a particular location or event by chance. Often used in the compound form 'passer-by' to describe an incidental witness to an occurrence.
A kind passer helped me pick up my dropped groceries.
The police are asking any passer who saw the accident to come forward with information.
The street performer relied on the generosity of the occasional passer, though most people hurried toward the station without glancing at his hat.
Commonly appears as part of the compound noun 'passer-by' (plural: 'passers-by').
three passer-bysthree passers-byIn compound nouns formed with a preposition, the plural 's' is added to the noun, not the preposition.