passer vs passerby

passer and passerby both are nouns.

Word	Noun	Adjective	Verb	Adverb
passer	Yes	No	No	No
passerby	Yes	No	No	No

As nouns, passer and passerby are synonyms defined as:

Other synonyms of passer include passer-by.

passer (noun)	passerby (noun)
(football) a ball carrier who tries to gain ground by throwing a forward pass	a person who passes by casually or by chance
a person who passes by casually or by chance
a student who passes an examination
a person who passes as a member of a different ethnic or racial group