115 entries under heavy topic. ×

14
acute(adjective, severe, harsh, important)
14
big(adjective, good, importance, important)
14
urgent(adjective, hard, tough, severe, difficult)
13
material(adjective, good, importance, big)
12
considerable(adjective, importance, big, important)
11
notable(adjective, great, extraordinary, importance, unusual)
10
major(adjective, great, unpleasant, important)
9
intense(adjective, severe, keen, warm, sensible)
9
no-nonsense(adjective, calm, dull, work, open)
8
bad(adjective, severe, nasty, offensive, unhappy)
8
somber(adjective, calm, dull, cool, severe)
7
perilous(adjective, bad, uncertain, significant)
6
businesslike(adjective, work, somber, efficient)
6
formidable(adjective, bad, hard, difficult, unpleasant)
6
menacing(adjective, bad, nasty, unpleasant)
6
threatening(adjective, bad, severe, unpleasant)
6
ugly(adjective, bad, nasty, offensive, unpleasant)
5
distressing(adjective, tough, severe, rough, difficult)
5
life-and-death(adjective, important, critical, vital)
5
strenuous(adjective, hard, severe, rough, difficult)
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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>