<p><strong>Noun</strong></p><ul><li>the ancient Roman god of fire and metalworking, identified with the Greek Hephaestus</li><li>a six-barrel, 20 mm U.S. Army antiaircraft gun system mounted on an armored personnel carrier and first deployed in 1968</li><li>a hypothetical planet nearest the sun whose existence was erroneously postulated to account for perturbations in Mercury's orbit</li></ul>