53 entries under solid topic. ×

16
impenetrable(adjective, close, hard, tough)
14
impervious(adjective, hard, fast, short)
11
tight(adjective, close, short, substantial)
10
compact(adjective, close, set, hard, tough)
7
close(adjective, set, hard, tough)
7
dense(adjective, set, hard, tough, firm)
7
impassable(adjective, dense, unaffected, unyielding)
7
thick(adjective, close, set, hard, tough)
6
firm(adjective, close, hard, fast)
6
nonporous(adjective, hard, rigid, resistant)
4
concrete(hard, rigid, density)
4
hard(adjective, set, tough, firm)
3
heavy(adjective, hard, rigid)
3
substantial(adjective, close, set, hard, tough)
2
compacted(adjective, dense, compressed)
2
compressed(adjective, set, hard, tough, firm)
2
concentrated(adjective, set, hard, tough, firm)
2
condensed(adjective, set, hard, tough, firm)
2
congested(adjective, close, short, substantial)
2
consolidated(adjective, close, short, substantial)
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APASmart Define. (2015). impermeable thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/impermeable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impermeable thesaurus" https://smartdefine.org/impermeable/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, impermeable thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/impermeable/thesaurus/synonyms>.
MLASmart Define. "impermeable thesaurus" 14 April 2015. Web. 22 September 2026. <https://smartdefine.org/impermeable/thesaurus/synonyms>