impregnable

About 0.67 uses per million words.

Meaning

1. adjective Of a fortress or other fortified place: able to withstand all attacks; impenetrable, inconquerable, unvanquishable.
2. adjective Too strong to be defeated or overcome; invincible.
3. adjective Capable of being impregnated; impregnatable.

Similar words

unassailable unconquerable inviolable inexpugnable invulnerable unattackable secure strong inaccessible spectacular

Often followed by

fortress to position and as by against in rock

Word family

impregnabilities impregnability impregnableness impregnablenesses impregnably