1 : the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second
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
3 : 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
4 : a period of time equal to 1/24th of a day
5 : (thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure
