602 entries under adjective topic. ×

10
tough(mean, strong, hard, severe)
10
unmerciful(mean, hard, tough, severe)
9
inhuman(animal, mean, hard, tough)
9
persevering(strong, tough, firm, determined)
9
pertinacious(strong, tough, firm, energetic)
9
rigorous(strong, hard, tough, severe)
9
set in stone(expression, idiom, mean, hard)
8
brutal(mean, strong, severe, evil)
8
callous(mean, hard, severe, evil)
8
eternal(continue, pause, steady, persistent)
8
heartless(mean, hard, severe, evil)
8
hidebound(severe, determined, resolute, persistent)
8
indomitable(strong, hard, tough, determined)
8
uninterrupted(continue, steady, persistent, constant)
8
unsparing(mean, strong, hard, tough)
8
unswayable(determined, resolute, rigid, obstinate)
7
dour(close, hard, severe, sharp)
7
ferocious(animal, mean, strong, severe)
7
hanging tough(expression, mean, hard, determined)
7
indefatigable(resolute, untiring)
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APASmart Define. (2015). relentless thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/relentless/thesaurus/synonyms
ChicagoSmart Define. 2015. "relentless thesaurus" https://smartdefine.org/relentless/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2015, relentless thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/relentless/thesaurus/synonyms>.
MLASmart Define. "relentless thesaurus" 24 June 2015. Web. 25 September 2026. <https://smartdefine.org/relentless/thesaurus/synonyms>