85 entries under hard topic. ×
| impenetrable(adjective, set, strong, firm) | |
| indurated(adjective, set, strong, firm) | |
| packed(adjective, set, strong, firm) | |
| rock hard(expression, adjective, strong, tough) | |
| tough inflexible(expression, adjective, strong, tough) |
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| APA | Smart Define. (2015). iron thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/iron/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "iron thesaurus" https://smartdefine.org/iron/thesaurus/synonyms (accessed September 28, 2026). |
| Harvard | Smart Define 2015, iron thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/iron/thesaurus/synonyms>. |
| MLA | Smart Define. "iron thesaurus" 14 April 2015. Web. 28 September 2026. <https://smartdefine.org/iron/thesaurus/synonyms> |