6
businesslike(adjective, work, heavy, somber, efficient)
6
deliberate(adjective, calm, set, cool, severe)
6
demure(adjective, calm, cool, modest, shy)
6
formidable(adjective, bad, hard, difficult, unpleasant)
6
heartfelt(adjective, open, keen, warm, honest)
6
hearty(adjective, complete, keen, warm, total)
6
integral(adjective, importance, main, extremely significant)
6
life-threatening(adjective, dangerous)
6
menacing(adjective, bad, nasty, unpleasant, heavy)
6
noble(adjective, importance, important, significant, grand)
6
pivotal(adjective, important)
6
reflective(adjective, set, deep, thoughtful, sober)
6
resolved(adjective, severe, firm, harsh, cruel)
6
threatening(adjective, bad, severe, unpleasant, heavy)
6
ugly(adjective, bad, nasty, offensive, unpleasant)
6
wholehearted(adjective, open, keen, warm, honest)
6
zealous(adjective, keen, warm, total, intense)
5
calm(adjective, cool, tough, sensible, relaxed)
5
devout(adjective, open, keen, warm, honest)
5
distressing(adjective, tough, severe, rough, difficult)
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APASmart Define. (2016). serious thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/serious/thesaurus/synonyms
ChicagoSmart Define. 2016. "serious thesaurus" https://smartdefine.org/serious/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2016, serious thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/serious/thesaurus/synonyms>.
MLASmart Define. "serious thesaurus" 24 February 2016. Web. 24 September 2026. <https://smartdefine.org/serious/thesaurus/synonyms>