137 entries under tough topic. ×

21
obstinate(adjective, mean, strong, hard)
19
grim(adjective, animal, appearance, mean, strong)
19
steadfast(adjective, strong, firm, determined)
17
cruel(adjective, appearance, mean, strong, hard)
17
remorseless(adjective, animal, mean, severe)
16
ruthless(adjective, animal, appearance, mean, hard)
16
unforgiving(adjective, mean, hard, severe)
16
unremitting(adjective, adverb, hard, continue)
15
tenacious(adjective, strong, firm, determined)
14
severe(adjective, appearance, mean, strong, hard)
14
dogged(adjective, appearance, mean, strong, hard)
14
hard-nosed(adjective, mean, strong, hard)
14
merciless(adjective, appearance, mean, hard)
13
hard(adjective, mean, strong, severe)
13
iron(adjective, mean, strong, hard)
13
pitiless(adjective, animal, mean, hard)
11
savage(adjective, animal, mean, strong, hard)
11
strict(adjective, strong, hard, severe)
10
austere(adjective, appearance, mean, strong, hard)
10
fierce(adjective, animal, mean, hard)
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APASmart Define. (2015). relentless thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/relentless/thesaurus/synonyms
ChicagoSmart Define. 2015. "relentless thesaurus" https://smartdefine.org/relentless/thesaurus/synonyms (accessed September 28, 2026).
HarvardSmart Define 2015, relentless thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/relentless/thesaurus/synonyms>.
MLASmart Define. "relentless thesaurus" 24 June 2015. Web. 28 September 2026. <https://smartdefine.org/relentless/thesaurus/synonyms>