72 entries under adjective topic. ×

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arcane(solid, dense)
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baffling(solid, dense)
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cabalistic(solid, dense)
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challenging(impossible, insuperable, insurmountable)
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close(solid, dense)
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concealed
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enigmatic(solid, dense)
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enigmatical(solid, dense)
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firm(solid, dense)
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hidden(solid, dense)
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inapproachable
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incognizable(solid, dense)
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indiscernible(solid, dense)
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inexplicable(solid, dense)
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inscrutable(solid, dense)
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mystic(solid, dense)
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overwhelming(hopeless, impossible, insuperable, insurmountable)
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sibylline(solid, dense)
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solid(dense, resistant, impervious)
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substantial(solid, dense)
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APASmart Define. (2015). impassable thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/impassable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impassable thesaurus" https://smartdefine.org/impassable/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2015, impassable thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/impassable/thesaurus/synonyms>.
MLASmart Define. "impassable thesaurus" 14 April 2015. Web. 24 September 2026. <https://smartdefine.org/impassable/thesaurus/synonyms>