- Definitions|2
- Thesaurus|716
- Abbreviations|0
| defendable(adjective, sound, reasonable, rational) | |
| defensible(sound, reasonable, rational, safety) | |
| fortified(adjective, firm, true, fixed, constant) | |
| impervious(adjective, secure, safe, snug, intact) | |
| inextinguishable(adjective, strength) | |
| insurmountable(adjective, impossible) | |
| irresistible(adjective, strength) | |
| mighty | |
| tough | |
| unquenchable(adjective, strength) | |
| absolute | |
| conceptive | |
| defended(adjective, secure, safe, snug, intact) | |
| dependable | |
| faithful(firm, true, fixed, constant, steadfast) | |
| good | |
| guarded(adjective, secure, safe, snug, intact) | |
| immovable(adjective, firm, true, fixed, resolute) | |
| incontestable | |
| indelible(firm, true, fixed, constant, steadfast) |
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| APA | Smart Define. (2015). impregnable thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/impregnable/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "impregnable thesaurus" https://smartdefine.org/impregnable/thesaurus/synonyms (accessed September 20, 2026). |
| Harvard | Smart Define 2015, impregnable thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/impregnable/thesaurus/synonyms>. |
| MLA | Smart Define. "impregnable thesaurus" 10 April 2015. Web. 20 September 2026. <https://smartdefine.org/impregnable/thesaurus/synonyms> |