<p><strong>Adjective:</strong></p><ul><li>Existing or occurring under water.</li><li>Designed to be used under water.</li><li>Located below a ship's waterline.</li></ul><p><strong>Adverb:</strong></p><ul><li>Beneath the water: to travel underwater.</li></ul><p><strong>Noun:</strong></p><ul><li>The water beneath the surface: cold currents in the underwater.</li><li>Underwaters: the depths, as of a sea, lake, etc.</li></ul>