2
overpowering
2
overwhelming
2
powerful
2
proof against(verb, expression, phrasal verb, strength, safety)
2
resistless
2
safeguarded(adjective, secure, safe, snug, intact)
2
shielded(adjective, secure, safe, snug, intact)
2
undefeatable
2
unkillable
2
unshakable(adjective, steady)
2
unstoppable
2
untouchable
1
accented
1
airtight
1
bombproof
1
buttoned up(expression, adjective, secure, safe, snug)
1
cherished(adjective, secure, safe, snug, intact)
1
close(adjective, firm, true, fixed, constant)
1
dangerous(adjective, hazardous, troubling)
1
deathless
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APASmart Define. (2015). impregnable thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/impregnable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impregnable thesaurus" https://smartdefine.org/impregnable/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2015, impregnable thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/impregnable/thesaurus/synonyms>.
MLASmart Define. "impregnable thesaurus" 10 April 2015. Web. 20 September 2026. <https://smartdefine.org/impregnable/thesaurus/synonyms>