202 entries under adjective topic. ×

5
unending(persistent, constant, continuous, endless)
5
unfaltering
5
unflagging
5
unmodifiable(set, secure, steady, fixed)
4
determined(hard, firm, resolute, rigid)
4
dogged(set, strong, hard, firm)
4
fast(calm, strong, solid, fixed)
4
intractable(set, hard, severe, rough)
4
ironclad
4
long-lasting(stable, constant, enduring, lasting)
4
resolved
4
rigorous(hard, resolute, rigid, inflexible)
4
set(calm, strong, secure, firm)
4
stiff(set, hard, severe, rough)
4
timeless(lasting, permanent, everlasting, unending)
4
tough(calm, strong, rough, solid)
4
unbending(hard, firm, rigid, inflexible)
4
uncompromising(hard, secure, rough, firm)
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undaunted
4
unvaried
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APASmart Define. (2015). immutable thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/immutable/thesaurus/synonyms
ChicagoSmart Define. 2015. "immutable thesaurus" https://smartdefine.org/immutable/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, immutable thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/immutable/thesaurus/synonyms>.
MLASmart Define. "immutable thesaurus" 10 April 2015. Web. 22 September 2026. <https://smartdefine.org/immutable/thesaurus/synonyms>