9
trusty(adjective, good, strong, honest, solid)
9
unanswerable(adjective, ideal, all time, the best)
9
unquestioned(adjective, complete, firm, sure, obedient)
8
absolutely
8
bound(adjective, definite, fixed, unquestionable, guaranteed)
8
definitive(adjective, clear, correct, plain, exact)
8
factual(adjective, correct, honest, pure, true)
8
flat(adjective, change, total, energetic, definite)
8
for sure(expression, idiom)
8
predetermined(adjective, determined, near, usual, regular)
8
some(adjective, pronoun, special, individual, various)
8
unchallengeable(adjective, ideal, all time, the best)
8
uncontested(adjective, ideal, all time, the best)
8
undisputable(adjective, certain, true, ideal, all time)
8
unqualified(adjective, clear, complete, flat, firm)
8
verifiable(adjective, reasonable, sensible, natural, obvious)
7
assuredly
7
authoritative(adjective, pure, original, real, genuine)
7
cogent(adjective, ideal, all time, the best)
7
definitely
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APASmart Define. (2016). certain thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/certain/thesaurus/synonyms
ChicagoSmart Define. 2016. "certain thesaurus" https://smartdefine.org/certain/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2016, certain thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/certain/thesaurus/synonyms>.
MLASmart Define. "certain thesaurus" 31 March 2016. Web. 20 September 2026. <https://smartdefine.org/certain/thesaurus/synonyms>