- Definitions|2
- Thesaurus|1.5k
- Abbreviations|0
98 entries under hard topic. ×
| tough(adjective, firm, solid, stiff) | |
| impervious(adjective, set, tough, solid) | |
| compact(adjective, close, set, tough) | |
| unfathomable(adjective, knowledge, obscure, difficult) | |
| dense(adjective, set, tough, firm) | |
| impermeable(adjective, close, tough, solid) | |
| solid(adjective, close, set, tough) | |
| thick(adjective, dull, close, tough) | |
| firm(adjective, close, set, solid) | |
| heavy(adjective, set, tough, solid) | |
| close(adjective, set, tough, solid) | |
| inaccessible(adjective, unfeeling, unsympathetic, prepared) | |
| condensed(adjective, set, tough, solid) | |
| stony(adjective, firm, stiff, unfeeling) | |
| compressed(adjective, set, tough, firm) | |
| nonporous(solid, rigid, resistant, impervious) | |
| packed(adjective, close, set, firm) | |
| substantial(adjective, close, set, strong) | |
| unyielding(adjective, set, tough, firm) | |
| concrete(adjective, set, tough, solid) |
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| APA | Smart Define. (2015). impenetrable thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/impenetrable/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "impenetrable thesaurus" https://smartdefine.org/impenetrable/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2015, impenetrable thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/impenetrable/thesaurus/synonyms>. |
| MLA | Smart Define. "impenetrable thesaurus" 10 April 2015. Web. 25 September 2026. <https://smartdefine.org/impenetrable/thesaurus/synonyms> |