1Attributive and in the genitive. Electricity. Designating a primary cell with a very low variation of voltage with temperature, used as a standard voltage source for calibration purposes.
historical Attributive Designating a system of film speeds based on exposure meters originally made by the Weston Electrical Instrument Company; designating a film speed expressed according to this system (also as postpositive).
Late 19th century. From the name of Edward Weston, English-born electrical engineer.