54
immovable(adjective, mean, strong, hard, secure)
54
tight(adjective, close, strong, hard, free)
54
uncompromising(adjective, mean, clear, hard, secure)
52
settled(adjective, characteristic, set, strong, secure)
51
durable(adjective, calm, strong, sound, secure)
50
set(verb, adjective, business, company, characteristic)
50
unbending(adjective, mean, clear, strong, hard)
49
enduring(adjective, calm, close, strong, sound)
49
stout(adjective, calm, strong, sound, tough)
48
permanent(adjective, calm, strong, secure, tough)
48
unalterable(adjective, characteristic, calm, strong, hard)
47
inexorable(adjective, mean, strong, hard, tough)
47
obdurate(adjective, strong, hard, secure, tough)
46
refractory(adjective, hard, strain, rough, harsh)
45
lasting(adjective, calm, strong, secure, tough)
45
stationary(adjective, strain, stable, firmness, labour)
44
unwavering(adjective, calm, close, strong, secure)
44
intransigent(adjective, determined, resolute, obstinate, stubborn)
44
invariable(adjective, calm, strong, secure, strain)
44
robust(adjective, strong, hard, sound, complete)
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APASmart Define. (2016). firm thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/firm/thesaurus/synonyms
ChicagoSmart Define. 2016. "firm thesaurus" https://smartdefine.org/firm/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2016, firm thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/firm/thesaurus/synonyms>.
MLASmart Define. "firm thesaurus" 31 March 2016. Web. 22 September 2026. <https://smartdefine.org/firm/thesaurus/synonyms>