1610s, "one's share or portion," from Latin quantum (plural quanta) "as much as, so much as; how much? how far? how great an extent?" neuter singular of correlative pronomial adjective quantus "as much" (see quantity). Introduced in physics directly from Latin by Max Planck, 1900; reinforced by Einstein, 1905. Quantum theory is from 1912; quantum mechanics, 1922; quantum jump is first recorded 1954; quantum leap, 1963, often figurative.
quantum quan·tum (kwŏn'təm)
n. pl. quan·ta (-tə)
The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
This amount of energy regarded as a unit.
A quantity or an amount.
A discrete, indivisible manifestation of a physical property, such as a force or angular momentum. Some quanta take the form of elementary particles; for example, the quantum of electromagnetic radiation is the photon, while the quanta of the weak force are the W and Z particles. See also quantum state.