ἀπαράβατος G531
aparábatos · ap-ar-ab'-at-os · Adjective
from Α (as a negative particle) and a derivative of παραβαίνω; not passing away, i.e. untransferable (perpetual):-- unchangeable.
1 Occurrence in the King James Bible
Hebrews 7:24But this man, because he continueth ever, hath an unchangeable priesthood.