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