<p><strong>Adjective</strong></p><ul><li>Said, done, or characterized by a lack of a sense of responsibility: His refusal to work shows him to be completely irresponsible.</li><li>Not capable of or qualified for responsibility, as due to age, circumstances, or a mental deficiency.</li><li>Not responsible, answerable, or accountable to higher authority: irresponsible as a monarch.</li></ul><p><strong>Synonyms</strong></p><ul><li>Undependable</li><li>Thoughtless</li><li>Unreliable</li><li>Neglectful</li><li>Slack</li><li>Lax</li></ul><p><strong>Noun</strong></p><ul><li>An irresponsible person.</li></ul>