26 entries under hardness topic. ×
| iron | |
| adamant(adjective, strength) | |
| steel | |
| bone | |
| brick | |
| cement | |
| concrete | |
| flint | |
| granite | |
| marble | |
| nail | |
| rock | |
| stone | |
| block | |
| board | |
| cartilage | |
| cast iron(expression, idiom) | |
| crag | |
| crystal | |
| deal board(expression, idiom) |
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| APA | Smart Define. (2015). oak thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/oak/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "oak thesaurus" https://smartdefine.org/oak/thesaurus/synonyms (accessed September 23, 2026). |
| Harvard | Smart Define 2015, oak thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/oak/thesaurus/synonyms>. |
| MLA | Smart Define. "oak thesaurus" 10 April 2015. Web. 23 September 2026. <https://smartdefine.org/oak/thesaurus/synonyms> |