74 entries under tough topic. ×

14
steely(adjective, strong, hard, firm)
12
iron(adjective, set, strong, hard)
9
uncompliant(adjective, firm, resist, determined)
8
fixed(adjective, severe, determined, resolute)
7
hardheaded(adjective, strong, hard, firm)
6
mulish(adjective, strong, hard, firm)
6
pigheaded(adjective, determined, resolute, stubborn)
6
stiff-necked(adjective, strong, hard, firm)
6
hard-nosed(adjective, strong, hard, determined)
6
steadfast(adjective, firm, determined, resolute)
6
strong(adjective, set, hard, strength)
6
sturdy(adjective, strong, hard, strength)
5
dogged(adjective, firm, determined, resolute)
5
rigorous(adjective, set, strong, hard)
4
bullheaded(adjective, strong, hard, severe)
4
rugged(adjective, set, strong, hard)
3
intractable(hard, firm, unreasonable, grim)
3
robust(adjective, strong, hard, strength)
2
dense(adjective, set, strong, hard)
2
durable(adjective, strong, firm, stiff)
11 years ago|6.5k views|share |citing 
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>