918 entries under adjective topic. ×

5
gloomy(dull, unhappy, dark, unpleasant)
5
life-and-death(heavy, important, critical, vital)
5
loyal
5
noteworthy(important, outstanding, prominent, remarkable)
5
parlous
5
passionate(complete, keen, warm, total)
5
saturnine(severe, unpleasant, horrible, disagreeable)
5
strenuous(hard, severe, rough, difficult)
4
contemplative(reasonable, thoughtful, sober, thinking)
4
burning(keen, warm, intense, passionate)
4
classical
4
collected(calm, cool, dark, relaxed)
4
cool(calm, sensible, unusual, relaxed)
4
decided(strong, firm, determined, resolute)
4
distinguished(great, unusual, important, famous)
4
drab(calm, dull, sensible, dark)
4
estimable(honest, pure, straight, grand)
4
extreme
4
faithful(open, firm, honest, true)
4
fatal
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APASmart Define. (2016). serious thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/serious/thesaurus/synonyms
ChicagoSmart Define. 2016. "serious thesaurus" https://smartdefine.org/serious/thesaurus/synonyms (accessed September 26, 2026).
HarvardSmart Define 2016, serious thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/serious/thesaurus/synonyms>.
MLASmart Define. "serious thesaurus" 24 February 2016. Web. 26 September 2026. <https://smartdefine.org/serious/thesaurus/synonyms>