Princeton's WordNet

1. hydrogen, H, atomic number 1(noun)

   a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe

   Synonyms:
   enthalpy, henry, heat content, hydrogen, atomic number 1, total heat

2. henry, H(noun)

   a unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second

   Synonyms:
   enthalpy, henry, heat content, hydrogen, atomic number 1, total heat

3. Planck's constant, h(noun)

   the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second

   Synonyms:
   enthalpy, atomic number 1, heat content, hydrogen, h, henry, total heat

4. H, h(noun)

   the 8th letter of the Roman alphabet

   Synonyms:
   enthalpy, henry, heat content, hydrogen, atomic number 1, total heat

5. heat content, total heat, enthalpy, H(noun)

   (thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure

   Synonyms:
   enthalpy, henry, heat content, hydrogen, atomic number 1, total heat