G0276–ἀμετάθετος–ametathetos

In this way God, being determined to show more abundantly to the heirs of the promise the immutability of his counsel, interposed with an oath;

ἀμετάθετον ametatheton “unchangeableness”

that by two immutable things, in which it is impossible for God to lie, we may have a strong encouragement, who have fled for refuge to take hold of the hope set before us.

ἀμεταθέτων, ametathetōn “unchangeable,”