adj. invulnerable, impenetrable, inviolable, unconquerable, invincible, unbeatable, indomitable, secure, safe, mighty, well-fortified The walls of the castle, sixteen feet thick, were impregnable
IMPREGNABLE
Meaning of IMPREGNABLE in English
Oxford thesaurus English vocab. Английский словарь Оксфорд тезаурус. 2012