What does "passer-by" mean?

A person who is passing by (that is, walking past).

What is a synonym for "passer-by"?

Common synonyms include: passer, passerby.

Pronounced //ˈpɑː.sə.baɪ//.

/ˈpɑː.sə.baɪ/ noun

noun ·Rare ·Advanced level

Noun

1
A person who is passing by (that is, walking past).
"When he tripped and fell in the street, several kind passers-by helped him up."
2
a person who passes by casually or by chance wordnet

"I enquired of a passer-by which road to take."

From passer + by. Compare bystander.