impregnable
Word family nounimpregnabilityadjectiveimpregnableadverbimpregnably
im·preg·na·ble /ɪmˈpreɡnəbəl/ adjectiveadj formal 1 DEFENDa building that is impregnable is so strong that it cannot be entered by force 〔建筑物〕攻不破的,固若金汤的 an impregnable fortress 坚不可摧的堡垒
2 STUBBORNstrong and impossible to change or influence 无法改变的,无法动摇的 her impregnable obstinacy 她的顽固不化
Origin impregnable (1400-1500) Old French imprenable “impossible to capture”, from prendre “to take”