from
The Collaborative International Dictionary of English v.0.48
Impregnable \Im*preg"na*ble\, a. [F. imprenable; pref. im- not +
prenable pregnable, fr. prendre to take, L. prehendere. See
{Comprehend}, {Get} to obtain.]
Not to be stormed, or taken by assault; incapable of being
subdued; able to resist attack; unconquerable; as, an
impregnable fortress; impregnable virtue.
[1913 Webster]
The man's affection remains wholly unconcerned and
impregnable. --South.
-- {Im*preg"na*ble*ness}, n. -- {Im*preg"na*bly}, adv.
[1913 Webster]