Pronunciation: (vul'kun),[key] —n. 1. the ancient Roman god of fire and metalworking, identified with the Greek Hephaestus.
2. Mil.a six-barrel, 20mm U.S. Army antiaircraft gun system mounted on an armored personnel carrier and first deployed in 1968.
3. Astron.a hypothetical planet nearest the sun whose existence was erroneously postulated to account for perturbations in Mercury's orbit.