a semiconductor diode usually used as a voltage regulator because its resistance breaks down at a precise, predetermined voltage level (), at which time it maintains a constant voltage while producing a sudden large increase in current
See zener diode in American Heritage Dictionary 4
or Ze·ner diode(zēˈnər)
noun
A silicon semiconductor device used as a voltage regulator because of its ability to maintain an almost constant voltage with a wide range of currents.