Synonyms for Unalterable (same or very similar meaning)
WordNet sense 1 (not capable of being changed or altered):
inalterable
WordNet sense 2 (not subject to alteration or change):
incommutable
WordNet sense 3 (remaining the same for indefinitely long times):
changeless
WordNet sense 4 (not changeable or subject to change):
unchangeable
From the ODE community, based on WordNet
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