65 entries under tough topic. ×

2
recalcitrant(firm, persistent, obstinate, stubborn)
2
solid(adjective, set, strong, hard)
2
thick(adjective, strong, hard, firm)
1
bound(verb, adjective, strong, firm)
1
bullhead(adjective, mean, hard, harsh)
1
callous(adjective, set, mean, strong, hard)
1
fixed(adjective, mean, strong, hard)
1
hard-boiled(adjective, mean, hard, harsh)
1
hard-hearted(adjective, mean, hard, harsh)
1
hard-nosed(adjective, mean, hard, harsh)
1
mean(adjective, hard, harsh, unfeeling)
1
mulish(adjective, mean, strong, hard)
1
perverse(adjective, mean, hard, firm)
1
pigheaded(adjective, mean, hard, firm)
1
staunch(adjective, set, strong, hard)
1
sure(adjective, strong, firm, solid)
1
thick-skinned(adjective, mean, hard, harsh)
1
tight(adjective, strong, firm, solid)
1
uncompassionate(adjective, mean, hard, harsh)
1
unimpressible(adjective, mean, hard, harsh)
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APASmart Define. (2015). iron thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/iron/thesaurus/synonyms
ChicagoSmart Define. 2015. "iron thesaurus" https://smartdefine.org/iron/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2015, iron thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/iron/thesaurus/synonyms>.
MLASmart Define. "iron thesaurus" 14 April 2015. Web. 20 September 2026. <https://smartdefine.org/iron/thesaurus/synonyms>