- Definitions|2
- Thesaurus|1.5k
- Abbreviations|0
308 entries under adjective topic. ×
| indestructible(firm, rigid, unyielding, steely) | |
| tough(hard, firm, solid, stiff) | |
| unbreakable(firm, solid, stiff, rigid) | |
| adamantine(set, tough, firm, stiff) | |
| rock-hard(firm, rigid, unyielding, steely) | |
| flinty(firm, rigid, unyielding, steely) | |
| impervious(set, hard, tough, solid) | |
| compact(close, set, hard, tough) | |
| obscure(dark, sophisticated, mysterious, complicated) | |
| unfathomable(hard, knowledge, obscure, difficult) | |
| incomprehensible(knowledge, obscure, solid, dark) | |
| inscrutable(knowledge, obscure, blank, sophisticated) | |
| dense(set, hard, tough, firm) | |
| impassable(solid, dense, unaffected, unyielding) | |
| impermeable(close, hard, tough, solid) | |
| solid(close, set, hard, tough) | |
| hard(tough, firm, solid, cruel) | |
| opaque(set, solid, heavy, deep) | |
| thick(dull, close, hard, tough) | |
| arcane(obscure, solid, strange, doubtful) |
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| APA | Smart Define. (2015). impenetrable thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/impenetrable/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "impenetrable thesaurus" https://smartdefine.org/impenetrable/thesaurus/synonyms (accessed September 24, 2026). |
| Harvard | Smart Define 2015, impenetrable thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/impenetrable/thesaurus/synonyms>. |
| MLA | Smart Define. "impenetrable thesaurus" 10 April 2015. Web. 24 September 2026. <https://smartdefine.org/impenetrable/thesaurus/synonyms> |