/ ˈhaɪdrədʒən; NAmE / noun
[ U ] ( symb H ) a chemical element. Hydrogen is a gas that is the lightest of all the elements. It combines with oxygen to form water.
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WORD ORIGIN
late 18th cent.: coined in French from Greek hudro- water + -genēs -born, of a specified kind, from gen- (root of gignomai be born, become, genos a kind).