a chemical element. Hydrogen is a gas that is the lightest of all the elements. It combines with oxygen to form water. 氢；氢气 Oxford Collocations DictionaryHydrogen is used before these nouns:- bomb
- fuel
- gas
- …
Word Originlate 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’).