an electronic device with two electrodes, as either an electron tube with an anode and a cathode or a transistor with a pn junction, used mainly as a rectifier since it conducts current in only one direction
See diode in American Heritage Dictionary 4
(dīˈōdˌ)
noun
An electronic device that restricts current flow chiefly to one direction.
An electron tube having a cathode and an anode.
A two-terminal semiconductor device used chiefly as a rectifier.