150 entries under adjective topic. ×

2
hard-core(strong, hard, tough, sturdy)
2
harsh(strong, hard, tough, severe)
2
heavy(strong, hard, tough, sturdy)
2
resolved(determined, resolute, uncompromising, unshakeable)
2
rocklike(firm, stiff, rigid)
2
severe(strong, hard, tough, harsh)
2
strict(set, strong, hard, tough)
2
unmoved
2
unwavering(determined, resolute, uncompromising, unshakeable)
2
valid
2
vigorous
1
atomic number 6
1
austere(strong, hard, tough, severe)
1
authoritarian(strong, hard, tough, sturdy)
1
callous(set, strong, hard, firm)
1
dead set(determined, resolute, uncompromising, unshakeable)
1
demanding
1
difficult
1
dyed-in-the-wool(set, strong, hard, tough)
1
hard-hearted
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APASmart Define. (2015). adamantine thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/adamantine/thesaurus/synonyms
ChicagoSmart Define. 2015. "adamantine thesaurus" https://smartdefine.org/adamantine/thesaurus/synonyms (accessed September 26, 2026).
HarvardSmart Define 2015, adamantine thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/adamantine/thesaurus/synonyms>.
MLASmart Define. "adamantine thesaurus" 10 April 2015. Web. 26 September 2026. <https://smartdefine.org/adamantine/thesaurus/synonyms>