122 entries under hard topic. ×
| mortified(adjective, strong, tough, severe) | |
| mulish(adjective, strong, tough, severe) | |
| obdurate(adjective, close, strong, tough) | |
| stiff-necked(adjective, strong, tough, severe) | |
| sturdy(adjective, strong, tough, solid) | |
| troublesome(adjective, tough, severe, rough) | |
| unrelenting(adjective, close, strong, tough) | |
| unsparing(adjective, close, strong, tough) | |
| vexatious(adjective, severe, rough, difficult) | |
| wearing(adjective, tough, rough, difficult) | |
| wearisome(adjective, tough, severe, rough) | |
| adamant(adjective, strong, tough, firm) | |
| adamantine(adjective, strong, tough, sturdy) | |
| dense(adjective, strong, tough, big) | |
| ferric(adjective, strong, tough, sturdy) | |
| ferrous(adjective, strong, tough, sturdy) | |
| immovable(adjective, strong, tough, sturdy) | |
| insensible(adjective, strong, tough, sturdy) | |
| robust(adjective, strong, tough, sturdy) | |
| steel(adjective, strong, tough, sturdy) |
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| APA | Smart Define. (2016). serious thesaurus. Retrieved September 27, 2026, from https://smartdefine.org/serious/thesaurus/synonyms |
| Chicago | Smart Define. 2016. "serious thesaurus" https://smartdefine.org/serious/thesaurus/synonyms (accessed September 27, 2026). |
| Harvard | Smart Define 2016, serious thesaurus, Smart Define, viewed 27 September, 2026, <https://smartdefine.org/serious/thesaurus/synonyms>. |
| MLA | Smart Define. "serious thesaurus" 24 February 2016. Web. 27 September 2026. <https://smartdefine.org/serious/thesaurus/synonyms> |