106 entries under tough topic. ×

11
pitiless(adjective, animal, mean, hard)
10
iron(adjective, mean, strong, hard)
10
steadfast(adjective, firm, determined, resolute)
8
firm(adjective, mean, strong, hard)
8
inhuman(adjective, animal, mean, hard)
8
steely(adjective, strong, hard, determined)
8
vindictive(adjective, mean, hard, severe)
7
determined(adjective, strong, hard, harsh)
7
dogged(adjective, appearance, mean, hard)
7
immovable(adjective, mean, strong, hard)
7
stiff-necked(adjective, mean, strong, hard)
7
uncompliant(adjective, firm, resist, determined)
6
savage(adjective, animal, mean, hard)
6
severe(adjective, appearance, mean, strong, hard)
6
unmerciful(adjective, mean, hard, severe)
4
bullheaded(adjective, strong, hard, firm)
4
mulish(adjective, mean, strong, hard)
4
uncompassionate(adjective, animal, mean, hard)
3
barbarous(adjective, animal, appearance, mean, hard)
3
hard-boiled(adjective, mean, strong, hard)
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APASmart Define. (2016). implacable thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/implacable/thesaurus/synonyms
ChicagoSmart Define. 2016. "implacable thesaurus" https://smartdefine.org/implacable/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2016, implacable thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/implacable/thesaurus/synonyms>.
MLASmart Define. "implacable thesaurus" 24 March 2016. Web. 21 September 2026. <https://smartdefine.org/implacable/thesaurus/synonyms>