From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Impregnable \Im*preg"na*ble\, a. [See Impregnate.] (Biol.)
Capable of being impregnated, as the egg of an animal, or the
ovule of a plant.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
impregnable
adj 1: immune to attack; incapable of being tampered with; "an
impregnable fortress"; "fortifications that made the
frontier inviolable"; "a secure telephone connection"
[syn: impregnable, inviolable, secure, strong,
unassailable, unattackable]
2: capable of conceiving [syn: conceptive, impregnable]
3: incapable of being overcome, challenged or refuted; "an
impregnable argument"; "impregnable self-confidence" [syn:
impregnable, inexpugnable]