53 entries under solid topic. ×

22
impenetrable(adjective, set, hard, tough)
16
impermeable(adjective, hard, fast, short)
13
impassable(adjective, unreasonable, useless, absurd)
11
hermetic(adjective, fast, short, dense)
7
hardened(noun, adjective, set, hard, tough)
6
compact(adjective, set, hard, tough)
5
firm(adjective, set, strong, hard, tough)
5
unyielding(adjective, hard, tough, rigid)
4
hard(adjective, set, tough, firm)
4
inviolable(adjective, secure, safe, dense)
3
inflexible(adjective, hard, tough, rigid)
3
thick(adjective, hard, rigid, dense)
3
tough(noun, adjective, set, strong, hard)
2
close(adjective, set, hard, tough)
2
dense(adjective, set, hard, tough)
2
rigid(adjective, hard, tough, detached)
2
stiff(adjective, set, hard, tough)
1
caked(adjective, set, heavy, deep)
1
clabbered(adjective, set, heavy, deep)
1
clotted(adjective, set, heavy, deep)
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APASmart Define. (2015). impervious thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/impervious/thesaurus/synonyms
ChicagoSmart Define. 2015. "impervious thesaurus" https://smartdefine.org/impervious/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, impervious thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/impervious/thesaurus/synonyms>.
MLASmart Define. "impervious thesaurus" 14 April 2015. Web. 22 September 2026. <https://smartdefine.org/impervious/thesaurus/synonyms>