16
unlikely(adjective, reasonable, unreasonable, likely)
12
unbelievable(adjective, unreasonable)
7
implausible(adjective, reasonable, unreasonable, likely)
7
inconceivable(adjective, reasonable, unreasonable, imaginable)
6
flimsy(adjective, strong, sound, implausible, unconvincing)
6
doubtful
5
far-fetched(adjective, hard)
5
illogical
5
improbable(adjective, unreasonable, likely)
5
impossible(adjective, unreasonable)
5
unreasonable
4
unimaginable(adjective, unreasonable)
3
incredible(adjective, bad, unremarkable)
3
fantastical
3
questionable
3
unconvincing
3
unthinkable
2
fantastic
2
preposterous
2
unsustainable
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APASmart Define. (2015). plausible thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/plausible/thesaurus/antonyms
ChicagoSmart Define. 2015. "plausible thesaurus" https://smartdefine.org/plausible/thesaurus/antonyms (accessed September 21, 2026).
HarvardSmart Define 2015, plausible thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/plausible/thesaurus/antonyms>.
MLASmart Define. "plausible thesaurus" 10 April 2015. Web. 21 September 2026. <https://smartdefine.org/plausible/thesaurus/antonyms>