4
strong(adjective, hard, tough, severe, sturdy)
4
stubborn(adjective, strong, hard, tough, severe)
4
violent
3
authoritarian(adjective, strong, hard, tough, severe)
3
caustic(adjective, severe)
3
cautious(adjective, wary, watchful)
3
clear-cut(noun, exact, precise, truth, accurate)
3
compressed
3
controlled
3
cutting(adjective, severe)
3
dead on(noun, exact, precise, accurate)
3
discriminating(adjective, close, correct, fine, solid)
3
distinct(noun, correct, solid, perfect, exact)
3
drastic(adjective, severe, harsh, cruel, brutal)
3
effortful(adjective, tough, rough, difficult, harsh)
3
express(noun, exact, precise, accurate)
3
fierce(adjective, hard, tough, harsh, intense)
3
fixed(adjective, hard, severe, stiff, rigid)
3
formidable(adjective, hard, tough, severe, rough)
3
hard-hearted(adjective, hard, tough, harsh, cruel)
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APASmart Define. (2016). rigorous thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/rigorous/thesaurus/synonyms
ChicagoSmart Define. 2016. "rigorous thesaurus" https://smartdefine.org/rigorous/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2016, rigorous thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/rigorous/thesaurus/synonyms>.
MLASmart Define. "rigorous thesaurus" 26 February 2016. Web. 21 September 2026. <https://smartdefine.org/rigorous/thesaurus/synonyms>