1. Noun.  The lightest chemical element (''symbol'' H) with an atomic number of 1 and atomic weight of 1.00794.
  2. Noun.  Molecular hydrogen (H2), a colourless, odourless and flammable gas at room temperature.
  3. Noun.  An atom of the element.
  4. Noun.  A sample of the element.

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This entry was last updated on RefTopia from its source on 3/20/2012.