81 entries under difficult topic. ×

50
strict(adjective, feature, strong, hard, tough)
41
severe(adjective, strong, hard, tough, correct)
34
precise(adjective, feature, hard, correct, right)
33
rigid(adjective, strong, hard, tough, correct)
32
stringent(adjective, hard, tough, severe, rough)
32
harsh(adjective, strong, hard, tough, severe)
31
meticulous(adjective, feature, hard, correct, slight)
28
stern(adjective, hard, tough, severe, rough)
27
scrupulous(adjective, feature, hard, tough, correct)
25
hard(adjective, strong, tough, severe, rough)
24
exacting(adjective, hard, tough, severe, fine)
23
correct(noun, adjective, hard, correct, right)
21
demanding(adjective, hard, severe, rough)
21
inflexible(adjective, strong, hard, tough, severe)
21
punctilious(adjective, hard, tough, correct, severe)
19
austere(adjective, strong, hard, tough, severe)
19
definite(noun, adjective, hard, correct, severe)
17
proper(adjective, hard, correct, right, severe)
17
stiff(adjective, hard, severe, rough)
15
uncompromising(adjective, hard, severe, rough)
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APASmart Define. (2016). rigorous thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/rigorous/thesaurus/synonyms
ChicagoSmart Define. 2016. "rigorous thesaurus" https://smartdefine.org/rigorous/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2016, rigorous thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/rigorous/thesaurus/synonyms>.
MLASmart Define. "rigorous thesaurus" 26 February 2016. Web. 20 September 2026. <https://smartdefine.org/rigorous/thesaurus/synonyms>