Lewis & Short

irrĕfrāgābĭlis (inr-), e, adj. [2. inrefragor], irrefragable (eccl. Lat.), Pseudo ug. ad Fr. Erem. Serm. 35.
Hence, adv.: irrĕfrāgābĭlĭter, inviolably: Catholici dogmatis fundamenta observare, Ven. Fort. Vit. Hilar. 1 praef. 1.