Английский Этимологический словарь - quantum

- 1619, "one's share or portion," from L. quantum "how much," neut. sing. of quantus "how great" (see quantity). Introduced in physics by Max Planck, 1900; reinforced by Einstein, 1905. Quantum theory is from 1912; quantum mechanics, 1922; quantum jump is first recorded 1955; quantum leap, 1970.