a glass apparatus in which hydrogen, generated from zinc and sulphuric acid, is burnt; used primarily as a demonstration (invented by Alessandro Volta)

(chemistry) hydrogen peroxide

(physics, astronomy) a spectral line of atomic hydrogen having a wavelength of about 21cm; used extensively in radio astronomy

a hydrogen electrode

(chemistry) the sulfur analogue of hydrogen peroxide, H₂S₂ / (erroneously) hydrogen sulfide

(chemistry, physics) an electrode in which hydrogen gas is adsorbed on platinum

(informal) dihydrogen monoxide (water (H₂O), but not hydrogen peroxide (H₂O₂) or the hydroxyl radical (-OH))

(chemistry) potassium bicarbonate

(inorganic chemistry, chiefly Britain) Alternative spelling of hydrogen sulfide

(inorganic chemistry) The compound sodium hydrogen arsenate.