Impossible to alter: the unalterable season of bitter cold in Siberia. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "unalterable" in a sentence
"No one form of Church polity as permanently unalterable is laid down in the New Testament though the apostolical order of bishops, or presbyters, and deacons, superintended by higher overseers (called bishops after the apostolic times), has the highest sanction of primitive usage."
"You will say, however, that facts remain unalterable; and that in some unlucky instance, in the changes and chances of human affairs, you may be proved to have been to blame."
"Hitherto most philosophy, the illegitimate heir of religion, had been a consolation and an apology for the constraints and limits of human existence which were represented as necessary; it had therefore been a prop supporting the existing social order, just because its definitions of freedom had been abstract and had claimed some kind of unalterable necessity."