passer-by vs passer

passer-by and passer both are nouns.

Word	Noun	Adjective	Verb	Adverb
passer-by	Yes	No	No	No
passer	Yes	No	No	No

As nouns, passer-by and passer are synonyms defined as:

Other synonyms of passer-by include passerby.

passer-by (noun)	passer (noun)
a person who passes by casually or by chance	(football) a ball carrier who tries to gain ground by throwing a forward pass
	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