114 entries under adjective topic. ×

16
impenetrable(close, hard, tough, solid)
14
impervious(hard, solid, fast, short)
11
tight(close, solid, short, substantial)
10
compact(close, set, hard, tough)
8
hermetic(tight, proof, impervious, impenetrable)
8
waterproof(water, tight, proof, impervious)
7
close(set, hard, tough, solid)
7
dense(set, hard, tough, firm)
7
impassable(solid, dense, unaffected, unyielding)
7
sealed(tight, proof, impervious, impenetrable)
7
thick(close, set, hard, tough)
7
watertight(tight, proof, impervious, impenetrable)
6
airtight(tight, proof, impervious, impenetrable)
6
firm(close, hard, solid, fast)
6
nonporous(hard, solid, rigid, resistant)
5
imperviable(unaffected, unyielding, unbending, resistant)
4
hard(set, tough, firm, solid)
4
proof(tight, impervious, hermetic)
3
closed
3
heavy(hard, solid, rigid)
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APASmart Define. (2015). impermeable thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/impermeable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impermeable thesaurus" https://smartdefine.org/impermeable/thesaurus/synonyms (accessed September 23, 2026).
HarvardSmart Define 2015, impermeable thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/impermeable/thesaurus/synonyms>.
MLASmart Define. "impermeable thesaurus" 14 April 2015. Web. 23 September 2026. <https://smartdefine.org/impermeable/thesaurus/synonyms>