/ɪmˈprɛɡnəbəl/
strong and impossible to defeat or change 不可战胜的；难以改变的 SYN invincible
The team built up an impregnable 5–1 lead.
这个队以 5:1 的绝对优势领先。
an impregnable building is so strongly built that it cannot be entered by force 坚不可摧的；牢不可破的
an impregnable fortress
坚不可摧的要塞