from The Century Dictionary.

  • Not pregnable; not to be taken or reduced by force: as, an impregnable fortress.
  • Not to be moved, shaken, or overcome; invincible: as, impregnable virtue.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective (Biol.) Capable of being impregnated, as the egg of an animal, or the ovule of a plant.
  • adjective Not to be stormed, or taken by assault; incapable of being subdued; able to resist attack; unconquerable

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective etc., also used figuratively Too strong to be penetrated.
  • adjective Capable of being impregnated.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adjective incapable of being overcome, challenged or refuted
  • adjective immune to attack; incapable of being tampered with
  • adjective capable of conceiving


from Wiktionary, Creative Commons Attribution/Share-Alike License

Ultimately from im- ("not"), French prendre ("to take"), and -able ("able to be the object of an action").

from Wiktionary, Creative Commons Attribution/Share-Alike License

From impregnate +‎ -able, ultimately from Latin impraegnatus ("made pregnant").


  • Charleston is a strongly fortified place and I think impregnable from the water side.

    Letter from Wright M. Carter to Young J. and Mollie Allen,May 6, 1861

  • Given the regular news reports of enterprise data lost through laptop theft, third party misfeasance, WEP hacking, loss of backup tapes, disgruntled employees, etc., it’s not like enterprise data is currently held in impregnable Kryptonite fortresses.

    Another Half-Dozen Half-Truths of the Cloud

  • It was this land side, containing the citadel and other works, which so impressed outsiders with the idea of impregnable strength.

    The Great Fortress : A chronicle of Louisbourg 1720-1760

  • You will storm that great fortress which men call impregnable -- you will storm it and you will vanquish it; and you will come home crowned with glory and honour!

    French and English A Story of the Struggle in America

  • I also knew that if we could by any means defend this doorway the murderers could get in nowhere else; for the palace is absolutely impregnable, that is, since the secret door by which Sorais had entered on that memorable night of attempted murder had, by Nyleptha's order, been closed up with masonry.

    Allan Quatermain

  • So he built an "impregnable" fortress atop the rock.

    Archive 2006-05-01

  • So he built an "impregnable" fortress atop the rock.


  • And never fear: the harmless, "impregnable" Iranians will be more than happy to aid their Shia religious brethren to victory in that battle.

    Archive 2005-12-01

  • And never fear: the harmless, "impregnable" Iranians will be more than happy to aid their Shia religious brethren to victory in that battle.

    The joys of Iraqi democracy . . . for Iran

  • Metcalfe said her department had put into place an "impregnable" security system which had been breached.

    ANC Daily News Briefing


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  • Contronymic in the sense: impossible to penetrate vs. penetrable, suseptible to impregnation.

    January 31, 2007


    "SkyTomb is impregnable"

    -Chilla,"MUMM-RA LIVES - PART III"

    March 18, 2008

  • It seems awfully weird that impregnable and impregnate mean kind of opposite things. You'd think it would better be inimpregnable.

    April 2, 2008

  • I think there are two different prefixes which both look like "im". The first is "not", and the second is roughly "in".

    April 2, 2008

  • better yet, the two meanings of "inflammable"--that which isn't flammable; that which can be inflamed.

    May 21, 2009

  • See unbearable.

    March 10, 2010