1
: not able to be captured by attack : very strong
an impregnable fortress
impregnable defenses
2
: not likely to be weakened or changed
an impregnable reputation
Her arguments seemed impregnable.
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“Impregnable.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/impregnable. Accessed 19 Jun. 2026.
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