84 entries under rational 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)
30
sober(adjective, calm, dull, quiet, cool)
23
sedate(adjective, calm, dull, cool, severe)
22
staid(adjective, calm, dull, set, cool)
9
no-nonsense(adjective, calm, dull, work, open)
8
composed(adjective, calm, cool, sensible, dark)
8
ruminative(adjective, reasonable, thoughtful, sober)
8
somber(adjective, calm, dull, cool, severe)
5
calm(adjective, cool, tough, sensible, relaxed)
4
collected(adjective, calm, cool, dark, relaxed)
4
drab(adjective, calm, dull, sensible, dark)
4
straightforward(open, honest, true, straight)
3
dull(adjective, tough, severe, dark, gloomy)
3
imperturbable(adjective, calm, cool, sensible, dark)
3
practical(adjective, calm, tough, plain, dark)
3
sensible(adjective, calm, relaxed, pure)
3
sound(adjective, calm, strong, honest, solid)
10 years ago|45k views|share |citing 
APASmart Define. (2016). serious thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/serious/thesaurus/synonyms
ChicagoSmart Define. 2016. "serious thesaurus" https://smartdefine.org/serious/thesaurus/synonyms (accessed September 23, 2026).
HarvardSmart Define 2016, serious thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/serious/thesaurus/synonyms>.
MLASmart Define. "serious thesaurus" 24 February 2016. Web. 23 September 2026. <https://smartdefine.org/serious/thesaurus/synonyms>