<p><strong>Adjective</strong></p><ul><li>Strong enough to resist or withstand attack; not to be taken by force, unconquerable: an impregnable fort.</li><li>Not to be overcome or overthrown: an impregnable argument.</li></ul><p><strong>Synonyms</strong></p><ul><li>Invulnerable</li></ul><p><strong>Antonyms</strong></p><ul><li>Vulnerable</li></ul><p><strong>Additional Notes</strong></p><ul><li>Indicating increased emphasis or force in grammar.</li><li>Certainly is an intensive adverb.</li><li>Myself in "I did it myself" is an intensive pronoun.</li></ul>