100 entries under restrained topic. ×

93
grave(adjective, calm, dull, quiet, help)
50
severe(adjective, calm, help, bad, strong)
39
solemn(adjective, calm, dull, quiet, cool)
37
earnest(noun, adjective, calm, dull, work)
31
sad(adjective, hard, difficult, complex, importance)
30
sober(adjective, calm, dull, quiet, cool)
23
sedate(adjective, calm, dull, cool, severe)
22
staid(adjective, calm, dull, set, cool)
10
steady(adjective, calm, set, cool, firm)
9
no-nonsense(adjective, calm, dull, work, open)
8
composed(adjective, calm, cool, sensible, dark)
8
somber(adjective, calm, dull, cool, severe)
5
calm(adjective, cool, tough, sensible, relaxed)
4
collected(adjective, calm, cool, dark, relaxed)
4
cool(adjective, calm, sensible, unusual, relaxed)
4
drab(adjective, calm, dull, sensible, dark)
4
serene(adjective, calm, cool, sensible, relaxed)
4
subdued(adjective, calm, quiet, severe, gentle)
4
unruffled(adjective, calm, cool, relaxed)
3
controlled(adjective, quiet, gentle, temperate)
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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>