<p><strong>Adjective</strong></p><ul><li>Phonetics: voiceless (consonant)</li><li>Mathematics: (of a quantity) not capable of being expressed in rational numbers; irrational.</li></ul><p><strong>Noun</strong></p><ul><li>Phonetics: a voiceless consonant (sonant).</li><li>Mathematics: a surd quantity.</li></ul>