Definition of: hydrogen

(hi′drə·jən) noun
The lightest of the elements (symbol H) occurring chiefly in combination with oxygen as water, and in hydrocarbons and other organic compounds. When isolated it is usually a colorless, odorless, tasteless, inflammable gas, lighter than air and liquefying under great pressure and low temperature.
—heavy hydrogen See DEUTERIUM. [<F hydrogène <Gk. hydōr water + gen-, stem of gignesthai be born; so called with ref. to the water formed by its combustion]
—hy·drog·e·nous (hī·droj′ə·nəs) adjective