impregnable
[adjective]
Synonyms: invulnerable, impenetrable, indestructible, invincible, secure, unassailable, unbeatable, unconquerable

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Contrasted words: exposed, open, susceptible
Related Words: safe, secure, defended, guarded, protected, safeguarded, shielded

[TahlilGaran] English Synonym Dictionary ▲

im‧preg‧na‧ble /ɪmˈpreɡnəbəl/ adjective formal
[Date: 1400-1500; Language: Old French; Origin: imprenable 'impossible to capture', from prendre 'to take']

1. a building that is impregnable is so strong that it cannot be entered by force:
an impregnable fortress

2. strong and impossible to change or influence:
her impregnable obstinacy

[TahlilGaran] Dictionary of Contemporary English ▲