97 entries under thoughtful topic. ×

93
grave(adjective, calm, dull, quiet, help)
50
severe(adjective, calm, help, bad, strong)
43
weighty(adjective, good, dull, hard, great)
39
solemn(adjective, calm, dull, quiet, cool)
37
earnest(noun, adjective, calm, dull, work)
30
sober(adjective, calm, dull, quiet, cool)
30
difficult(adjective, hard, tough, easy, harsh)
26
profound(adjective, hard, difficult, complex, deep)
23
sedate(adjective, calm, dull, cool, severe)
22
staid(adjective, calm, dull, set, cool)
20
grim(adjective, dull, strong, hard, tough)
19
heavy(adjective, strong, hard, great, tough)
15
sincere(noun, adjective, open, keen, warm)
11
deep(adjective, keen, important, significant)
10
steady(adjective, calm, set, cool, firm)
9
no-nonsense(adjective, calm, dull, work, open)
9
resolute(adjective, severe, firm, sensible, harsh)
8
determined(adjective, set, strong, firm, total)
8
honest(adjective, set, open, true, natural)
8
intent(adjective, firm, determined, sober)
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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>