1
staunch(adjective, strong, firm, true, fixed)
1
steely
1
sturdy
1
sure(adjective, firm, true, fixed, resolute)
1
swift
1
tenacious(adjective, firm, true, fixed, constant)
1
tended(adjective, secure, safe, snug, intact)
1
unafraid
1
unasked
1
undamaged(adjective, secure, safe, snug, intact)
1
undampable
1
under lock and key(expression, idiom, secure, safe, snug)
1
undestroyable
1
undying
1
unharmed(adjective, secure, safe, snug, intact)
1
unhurt(adjective, secure, safe, snug, intact)
1
uninjured(adjective, secure, safe, snug, intact)
1
unmolested(adjective, secure, safe, snug, intact)
1
unscathed(adjective, secure, safe, snug, intact)
1
unsubduable
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APASmart Define. (2015). impregnable thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/impregnable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impregnable thesaurus" https://smartdefine.org/impregnable/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2015, impregnable thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/impregnable/thesaurus/synonyms>.
MLASmart Define. "impregnable thesaurus" 10 April 2015. Web. 21 September 2026. <https://smartdefine.org/impregnable/thesaurus/synonyms>