60 entries under noun topic. ×

8
imperviousness(protection, security, rigidity, hardness)
8
obscurity(depth, incomprehensibility)
6
density(mass, protection, security, rigidity)
6
opacity
5
impenetrableness
4
impermeability(protection, security, rigidity, hardness)
4
solidity(mass, protection, security, rigidity)
3
thickness(mass, bulk, density, impermeability)
2
callousness
2
closeness(mass, bulk, density, thickness)
2
complexity(incomprehensibility, elaborateness)
2
crowdedness(mass, bulk, density, thickness)
2
difficulty
2
firmness(rigidity, hardness)
2
hardness(protection, security, cruelty, rigidity)
2
inscrutability
2
intricacy
2
resistance(protection, security, rigidity, hardness)
2
toughness(protection, security, rigidity, hardness)
1
consistency(mass, bulk, density, thickness)
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APASmart Define. (2015). impenetrability thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/impenetrability/thesaurus/synonyms
ChicagoSmart Define. 2015. "impenetrability thesaurus" https://smartdefine.org/impenetrability/thesaurus/synonyms (accessed September 26, 2026).
HarvardSmart Define 2015, impenetrability thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/impenetrability/thesaurus/synonyms>.
MLASmart Define. "impenetrability thesaurus" 14 April 2015. Web. 26 September 2026. <https://smartdefine.org/impenetrability/thesaurus/synonyms>