ὅς

• Agrees with its antecedent in gender and number; its case comes from its role in its own clause (though it is often attracted to the antecedent’s case).
• Always accented, unlike the article: ὅ “which” vs ὁ “the”, ἥ vs ἡ, οἵ vs οἱ, αἵ vs αἱ.
• ἀφ’ οὗ “since”, ἕως οὗ “until”, ἀνθ’ ὧν “because”.

Forms in bold occur in the New Testament; the others complete the pattern. A dash (—) marks a form that does not exist.

From Appendix B of the Greek and Latin with Jerome study companion · PDF page 263 · open the PDF here