Galatians 3:15 ἀδελφοί, κατὰ ἄνθρωπον λέγω· ὅμως ἀνθρώπου κεκυρωμένην διαθήκην οὐδεὶς ἀθετεῖ ἢ ἐπιδιατάσσεται.
Brothers, speaking of human terms, though it is only a man's covenant, yet when it has been confirmed, no one makes it void, or adds to it.
Noun: Accusative Singular Feminine

Galatians 3:17 τοῦτο δὲ λέγω· διαθήκην προκεκυρωμένην ὑπὸ τοῦ θεοῦ ὁ μετὰ τετρακόσια καὶ τριάκοντα ἔτη γεγονὼς νόμος οὐκ ἀκυροῖ εἰς τὸ καταργῆσαι τὴν ἐπαγγελίαν.
Now I say this. A covenant confirmed beforehand by God in Christ, the law, which came four hundred thirty years after, does not annul, so as to make the promise of no effect.
Noun: Accusative Singular Feminine

Hebrews 8:8 μεμφόμενος γὰρ αὐτοὺς λέγει, ἰδοὺ ἡμέραι ἔρχονται λέγει κύριος, καὶ συντελέσω ἐπὶ τὸν οἶκον Ἰσραὴλ καὶ ἐπὶ τὸν οἶκον Ἰούδα διαθήκην καινήν,
For finding fault with them, he said, "Behold, the days come," says the Lord, "that I will make a new covenant with the house of Israel and with the house of Judah;
Noun: Accusative Singular Feminine

Hebrews 8:9 οὐ κατὰ τὴν διαθήκην, ἣν ἐποίησα τοῖς πατράσιν αὐτῶν ἐν ἡμέρᾳ ἐπιλαβομένου μου τῆς χειρὸς αὐτῶν ἐξαγαγεῖν αὐτοὺς ἐκ γῆς Αἰγύπτου, ὅτι αὐτοὶ οὐκ ἐνέμειναν ἐν τῇ διαθήκῃ μου, κἀγὼ ἠμέλησα αὐτῶν, λέγει κύριος·
not according to the covenant that I made with their fathers, in the day that I took them by the hand to lead them out of the land of Egypt; for they didn't continue in my covenant, and I disregarded them," says the Lord.
Noun: Accusative Singular Feminine