<p><strong>Adjective</strong></p><ul><li>curved like a segment of the interior of a circle or hollow sphere; hollow and curved</li><li>(of a polygon) having at least one interior angle greater than 180°</li><li>Obsolete. hollow</li></ul><p><strong>Noun</strong></p><ul><li>a concave surface, part, line, or thing</li><li>Machinery. a concave piece, as one against which a drum rotates</li></ul><p><strong>Verb</strong></p><ul><li>(used with object) to make concave</li></ul>