What is the meaning of Hydrogen?

The lightest chemical element (symbol H), with an atomic number of 1 and atomic weight of 1.008.

An atom of this element.

Molecular hydrogen (sense 1; symbol H₂), a colourless, odourless and flammable gas at room temperature.

A molecule of this molecular species.

Synonym of protium (“the lightest and most common isotope of hydrogen (sense 1; symbol H, H, or 11H), as contrasted with deuterium and tritium”).

hydrogen

hydrogen (chemical element, symbol H)

hydrogen (chemical element, symbol H)

hydrogen

Source: wiktionary.org