- Definitions|2
- Thesaurus|1.5k
- Abbreviations|0
55 entries under stiff topic. ×
| tough(adjective, hard, firm, solid) | |
| unbreakable(adjective, firm, solid, rigid) | |
| adamantine(adjective, set, tough, firm) | |
| impervious(adjective, set, hard, tough, solid) | |
| compact(adjective, close, set, hard, tough) | |
| dense(adjective, set, hard, tough, firm) | |
| solid(adjective, close, set, hard, tough) | |
| hard(adjective, tough, firm, solid, cruel) | |
| opaque(adjective, set, solid, heavy, deep) | |
| thick(adjective, dull, close, hard, tough) | |
| firm(adjective, close, set, hard, solid) | |
| deep(adjective, set, obscure, solid, heavy) | |
| heavy(adjective, set, hard, tough, solid) | |
| close(adjective, set, hard, tough, solid) | |
| condensed(adjective, set, hard, tough, solid) | |
| stony(adjective, hard, firm, unfeeling) | |
| compressed(adjective, set, hard, tough, firm) | |
| rocky(adjective, set, firm, compact) | |
| packed(adjective, close, set, hard, firm) | |
| unyielding(adjective, set, hard, tough, firm) |
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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> |