4
unquestionable(adjective, definite)
3
actual
3
authentic(good, sound, right, reasonable, rational)
3
authoritative(good, sound, right, reasonable, rational)
3
certain(adjective, strong, reasonable, easy, sensible)
3
confirmed(good, sound, right, reasonable, rational)
3
consistent(reasonable, sensible, natural, normal, valid)
3
convincing(sound, reasonable, rational)
3
enduring(adjective, calm, strong, sound, secure)
3
faithful(correct, proper, moral)
3
genuine(good, sound, right, reasonable, rational)
3
hard
3
honest
3
justifiable(adjective, sound, reasonable, rational, valid)
3
lasting(calm, strong, solid, steady, substantial)
3
lawful(adjective, good, sound, right, reasonable)
3
legal(good, sound, right, reasonable, rational)
3
potent(good, strong, sound, right, reasonable)
3
powerful(adjective, good, strong, great, sound)
3
proven(adjective, sound, reasonable, rational, logical)
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APASmart Define. (2016). well-founded thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/well-founded/thesaurus/synonyms
ChicagoSmart Define. 2016. "well-founded thesaurus" https://smartdefine.org/well-founded/thesaurus/synonyms (accessed September 26, 2026).
HarvardSmart Define 2016, well-founded thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/well-founded/thesaurus/synonyms>.
MLASmart Define. "well-founded thesaurus" 29 March 2016. Web. 26 September 2026. <https://smartdefine.org/well-founded/thesaurus/synonyms>