WordNet sense 1 (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):

hydrogen, atomic number 1

WordNet sense 2 (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):

henry

WordNet sense 3 (the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second):

Planck's constant

WordNet sense 4 (the 8th letter of the Roman alphabet):

letter h

WordNet sense 5 ((thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure):

enthalpy, heat content, total heat