- hydrogen, H, atomic number 1 - a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe
--1 is a kind of chemical element, element; gas
--1 is a substance of water, H2O
--1 has particulars: tritiumDerived form: verb hydrogenate1