63 entries under protected topic. ×

47
strong(adjective, sound, reasonable, strain, rational)
41
firm(adjective, strain, true, firmness, constant)
37
sound(adjective, reasonable, strain, firm, true)
37
stable(adjective, strain, firm, true, firmness)
22
fast(adjective, strain, firm, firmness, constant)
19
tight(adjective, strain, firm, true, firmness)
18
immune(adjective, strain, firmness, safe, labour)
18
steady(adjective, strain, firmness, safe, labour)
14
secure(adjective, sound, reasonable, firm, true)
14
unassailable(adjective, strong, secure, resolute, safe)
12
invulnerable(adjective, strong, secure, resolute, safe)
11
inviolable(adjective, secure, safe, snug, intact)
7
safe(adjective, secure, harm, unquestionable, snug)
4
solid(adjective, safe, unyielding, sheltered)
3
fortified(adjective, firm, true, fixed, constant)
3
impervious(adjective, secure, safe, snug, intact)
2
defended(adjective, secure, safe, snug, intact)
2
guarded(adjective, secure, safe, snug, intact)
2
immovable(adjective, firm, true, fixed, resolute)
2
safeguarded(adjective, secure, safe, snug, intact)
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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>