6
tenable(adjective, reasonable, justified, defensible)
6
true(sound, reasonable, rational, absolute, valid)
5
sane(adjective, reason, sane)
5
set(adjective, calm, strong, solid, steady)
5
steady(adjective, calm, strong, sound, secure)
5
sturdy(adjective, calm, strong, sound, secure)
5
sure(adjective, calm, strong, reasonable, sensible)
5
weighty(good, sound, right, reasonable, rational)
4
balanced(adjective, calm, strong, secure, easy)
4
credible(good, sound, right, reasonable, rational)
4
deep-rooted(adjective, calm, strong, solid, steady)
4
dependable
4
durable(adjective, calm, strong, sound, secure)
4
factual
4
fast(adjective, calm, strong, secure, solid)
4
logical(adjective, good, sound, right, reasonable)
4
proper(adjective, correct, reasonable, moral, valid)
4
rooted(strong, secure, stable)
4
stout(adjective, calm, strong, sound, secure)
4
trustworthy(good, sound, right, reasonable, rational)
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APASmart Define. (2016). well-founded thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/well-founded/thesaurus/synonyms
ChicagoSmart Define. 2016. "well-founded thesaurus" https://smartdefine.org/well-founded/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2016, well-founded thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/well-founded/thesaurus/synonyms>.
MLASmart Define. "well-founded thesaurus" 29 March 2016. Web. 25 September 2026. <https://smartdefine.org/well-founded/thesaurus/synonyms>