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Impregnable

adj. resilient, capable formal

What it means

Meaning 1

So strongly protected that attack, entry, or defeat appears impossible.

Reach for it when using forceful praise for a defense or position that has resisted serious challenge

The hilltop storehouse seemed impregnable behind its layered stone walls.

Meaning 2

Unable to be successfully challenged or refuted.

Reach for it when describing an argument whose evidence closes every material gap

Independent records made the chronology nearly impregnable.

Words to choose between 6

By register, from playful at the top to literary at the bottom, and by meaning across. Tap a word to see when it fits.
Meaning 1Meaning 2
playful
everyday
professional
formal

Meaning 1: So strongly protected that attack, entry, or defeat appears impossible.

  • everyday

    secure

    Fits when reasonable protection is the honest practical claim

    Careful Secure is deliberately weaker and better when no absolute test exists.

  • professional

    fortified

    Fits when deliberate defenses have been added

    Careful Fortified describes preparation and stops short of claiming those defenses cannot fail.

  • professional

    impenetrable

    Fits when entry through a boundary is physically blocked

    Careful Impenetrable may mean difficult to understand rather than secure.

  • formal

    invulnerable

    Fits when exposure to harm appears absent

    Careful Invulnerable can describe a person or system and is less tied to defenses.

Meaning 2: Unable to be successfully challenged or refuted.

  • playful

    watertight

    Fits when informal praise should stress that an argument has no obvious leak

    Careful Watertight sounds casual and should not overstate evidence with unresolved limits.

  • formal

    unassailable

    Fits when criticism or attack cannot find a viable opening

    Careful Unassailable fits claims and reputations better than a physical enclosure.

Opposites 3

  • exposed
  • penetrable
  • refutable

Common phrases 3

  • impregnable fortress

    The ridge made the fortress appear impregnable from the valley.

  • seem impregnable

    No network should be assumed to seem impregnable after one audit.

  • impregnable argument

    The dated records gave her an impregnable argument for preservation.

Usage notes

Keep in mind

Impregnable is an absolute claim. Practical security writing should prefer a bounded tested claim unless failure has genuinely been ruled out.

Definitions and examples are written for this site. How words are chosen Recording: Vealhurl, Southern England accent, from Wikimedia Commons, CC BY-SA 4.0 Updated