hydrogen
[ˈhaɪdrɪdʒən]
n
a. 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. Symbol: H; atomic no: 1; atomic wt: 1.00794; valency: 1; density: 0.08988 kg/m³; melting pt: –259.34°C; boiling pt: –252.87°C
See also: deuterium, tritium
b. (as modifier)
hydrogen bomb
etymology C18: from French hydrogène, from hydro- + -gen; so called because its combustion produces water
