A flammable colourless gas that is the lightest and most abundant element in the universe. It occurs mainly in water and in most organic compounds and is used in the production of ammonia and other chemicals, in the hydrogenation of fats and oils, and in welding.
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
