74 entries under tough topic. ×

33
inexorable(adjective, strong, hard, resist)
32
inflexible(adjective, strong, hard, firm)
32
unrelenting(adjective, strong, hard, resist)
31
adamant(adjective, strong, hard, firm)
31
stubborn(adjective, characteristic, quality, strong, hard)
30
unyielding(adjective, strong, hard, firm)
26
flinty(adjective, strong, hard, firm)
26
obdurate(adjective, strong, hard, resist)
26
rigid(adjective, strong, hard, severe)
26
uncompromising(adjective, resist, determined, resolute)
25
unbending(adjective, strong, hard, resist)
25
unbreakable(adjective, strong, severe, firm)
24
relentless(adjective, strong, hard, resist)
21
hard(adjective, strong, strength, firm)
21
impenetrable(adjective, set, firm, stiff)
20
firm(adjective, strong, hard, determined)
17
immovable(adjective, strong, hard, cruel)
17
implacable(adjective, strong, hard, resist)
15
grim(adjective, strong, hard, resist)
14
determined(adjective, strong, hard, severe)
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APASmart Define. (2015). adamantine thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/adamantine/thesaurus/synonyms
ChicagoSmart Define. 2015. "adamantine thesaurus" https://smartdefine.org/adamantine/thesaurus/synonyms (accessed September 28, 2026).
HarvardSmart Define 2015, adamantine thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/adamantine/thesaurus/synonyms>.
MLASmart Define. "adamantine thesaurus" 10 April 2015. Web. 28 September 2026. <https://smartdefine.org/adamantine/thesaurus/synonyms>