3
heavy(adjective, strong, hard, tough, severe)
3
implacable(adjective, strong, hard, tough, harsh)
3
inelastic
3
intricate(adjective, tough, rough, difficult, heavy)
3
mean(adjective, tough, severe, rough, difficult)
3
murderous(adjective, hard, tough, harsh, cruel)
3
on target(noun, exact, precise, accurate)
3
painful(adjective, hard, tough, severe, difficult)
3
peremptory(adjective, severity, authoritative, overbearing)
3
perfect(noun, exact, precise, accurate)
3
pitiless(adjective, hard, tough, severe, harsh)
3
prim(adjective, thoughtful, sober, cautious, prudent)
3
right on(noun, exact, precise, accurate)
3
ruthless(adjective, hard, tough, harsh, unpleasant)
3
scientific(adjective, close, correct, solid, exact)
3
specific(noun, correct, solid, perfect, exact)
3
steep(adjective, severe, stringent, drastic)
3
tart(adjective, severe)
3
taut(adjective, rigid)
3
taxing(adjective, heavy)
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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>