If you describe a building or other place as impregnable, you mean that it cannot be broken into or captured.
例句
The old Dutch fort with its thick high walls looks virtually impregnable...古老的荷蘭城堡城墻又厚又高,看起來幾乎固若金湯。In those impregnable mountains, the guerrillas could hold out for years.在那些易守難攻的大山里，游擊隊可以堅持很多年。
ADJ
不可戰勝的;不可撼動的
If you say that a person or group is impregnable, or their position is impregnable, you think they cannot be defeated by anyone.
例句
The Bundesbank's seemingly impregnable position has begun to weaken.德意志聯邦銀行看似不可撼動的地位開始削弱了。
英漢詞典釋義
adj.
攻不破的, 堅不可摧的
an impregnable castle攻不破的堡壘The lofty walls of the castle seemed impregnable.這座城堡的高墻似乎堅不可摧。They will establish impregnable fortresses.他們將建造堅不可摧的城堡。
英英詞典釋義
Adjective
1. able to withstand attack;
"an impregnable fortress""fortifications that made the frontier inviolable"