Question

Which possessive noun is correct, passer's-by or passer-by's?

Answer 1

The correct form is passer-by's.

Explanation:

This combination of two words (called a compound word), is thought of as one single word. So the grammatical rules for possessive would still apply to it.

`"passer-by = singular"`

The possessive singular is `color(red)"'s"` at the end of the word, so the possessive would be:

`"passer-by's = singular possessive"`

If you want to know more about possessives, the answer to this question that I gave gives more depth!