'Impregnable' definitions:

Definition of 'impregnable'

From: WordNet
adjective
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]
adjective
Capable of conceiving [syn: conceptive, impregnable]
adjective
Incapable of being overcome, challenged or refuted; "an impregnable argument"; "impregnable self-confidence" [syn: impregnable, inexpugnable]

Definition of 'Impregnable'

From: 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]

Definition of 'Impregnable'

From: 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]