1 : (thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure; "enthalpy is the amount of energy in a system capable of doing mechanical work"
2 : 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
3 : 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
