H

(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: hydrogen, atomic number 1.

(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: henry.

(noun) the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second. Synonyms: Planck's constant, h.

(noun) the 8th letter of the Roman alphabet. Synonyms: h.

(noun) (thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure. Synonyms: heat content, total heat, enthalpy. Example: "Enthalpy is the amount of energy in a system capable of doing mechanical work."